Nursing care plan for multiple pregnancy

INTRODUCTION

The high-risk nature of multiple pregnancy had long been a feature of scholarly reviews of this topic. Past interpretations of this risk, however, often were affected by a variety of biases, including small numbers, faulty ascertainment methodologies, insufficient analytic power, use of inappropriate outcome measures, or a combination of these factors. More recent publications on twin gestations have utilized national data obtained from birth certificates or representative national population samples. These data have provided a far more accurate picture of specific aspects of the risks associated with multiple pregnancy than could have been attained in the past. Moreover, these samples have been sufficiently large so that appropriate comparison groups could be constituted and clinical differences characterized by their statistical validity or lack thereof.

One prime example of the “new research” in multiple gestations is an analysis of the 1985 to 1988 US linked birth/infant death data sets by Powers and Wampler.1 A total of 138,779 twin pregnancies, each ending in the delivery of two liveborn infants, were described. The large numbers of both white and black women included in the study serve to refine prior estimations of risk by using twin pair gender and maternal age/race as study variables. According to this methodology, male/female pairs born to white women more than 28 years old have the lowest risk, whereas male/male pairs born to black women less than 28 years old are at higher risk.1 Analyses such as these will be increasingly useful in the future, not only to clarify our concept of “risk,” but also to introduce programs to compensate for it. Unfortunately, these large analyses have studied factors such as maternal age, race, and sex of twins and have failed to analyze twin outcomes by chorionicity [see later discussion], which is a major factor leading to adverse outcome.

DEMOGRAPHIC CONSIDERATIONS

According to Boklage,2 “most human conceptions fail before clinical recognition and thus never reach term.” This is true for singletons as well as twins, although the risk of total pregnancy loss is disproportionately weighted against twins. Available data indicate survival for no more than 1 in 4 natural singleton conceptions; in contrast, survivability declines drastically to 1 in 50 natural twin conceptions.2 Boklage's projections further suggest that 1 of every 8 human conceptions begins as a twin conception, and that for each twin pair born alive 10 to 12 twin pregnancies that began as twins result in single births. An extensive discussion of this natural reduction process, popularly known as the vanishing twin syndrome [or phenomenon], is beyond the scope of this chapter, as is discussion of the question of whether twins are “accidents of nature” or “congenital anomalies."3,4 For completeness, however, the commonly quoted disappearance rate assessed by Landy and associates is 21%.4

In the United States, comprehensive data on birth plurality have been compiled, albeit in an irregular manner, from live birth certificates since 1917. Summaries of these data have been published annually since that time, incorporating a minimum lag time of 2 or more years. Live birth and fetal death records were matched before 1959. Since then, however, this process has been abandoned. The last revision of the standard US birth certificate was promulgated in 1989. Although extensively modified, it failed to inquire whether conceptions had been achieved by natural or artificial means.5 The next revision of this document is not expected until 1999.

In the United States, the number of live twin births and the ratio of twin births per 1000 live births began to increase in the early 1970s. This trend continues and holds true for all races combined, whites and/or blacks separately and the category of “all others.” Detailed analyses of these changes have been prepared by Taffel from unpublished governmental sources.6 Table 1 summarizes this information and demonstrates that all racial groups contribute a portion of the general increase in twin births, albeit not to the same degree. Such findings support the contention that the increases in the number of multiple births are not restricted to racial and social groups with better access to medical care, especially fertility-enhancing agents, but rather represent a broad global phenomenon.

TABLE 1. Changes in the Absolute Numbers and Ratio of Twin Births, USA, 1973 and 1992
Click here to view Table 1.

Figure 1 provides an additional perspective of the changes occurring in recent years. Between 1960 and 1973, singleton and twin birth rates declined in a parallel fashion [twins declined from 1 in 49 to 1 in 55 births], whereas triplet births were fairly constant [1 in 3624 to 1 in 3323]. The conclusion of the “baby booms” that followed World War II and the Korean War, respectively, was followed by the present “epidemic” in multiple births starting in 1973. The rate of twin births increased at twice that of singletons [65% vs 32%]; the rate of births of triplets and higher order multiples increased at seven times that of singletons [221% vs 32%].7

As depicted in Table 1, the changes in the total numbers of twins did not affect all groups of the population equally.7 Whereas the multiple birth ratio increased in every age category in whites and blacks, there were substantial differences between these two racial groups [Fig. 2]. Of equal or greater importance, as shown in Figure 3 and Figure 4, respectively, a 25% increase in the proportion of preterm births was recorded among multiple births [from 39.3% to 49.1%] compared to singleton births [a 13% increase, from 8.6% to 9.7%].7 Much of this overall increase, however, may have related to the growing number of triplet and higher order births, because the characterization of “preterm” was assigned to 87.8% of triplet and higher order births, compared to 47.9% of twin births and 9.7% of singleton births, respectively, in 1990.7

Figure 4 demonstrates differences in birth weight distributions by plurality.7 The obvious differences in gestational age and weight at birth based on plurality represent a principal feature of the risks attributable to multiples compared to singletons—risks that continue later in life.8 Simply stated, the relative risks of adverse health outcomes are heavily weighted against multiples compared to singletons [Table 2]. Two independent investigations, both using US linked birth/infant death data sets, augment the findings shown in Table 2. The first relied on data from the 1985 and 1986 birth cohorts and used singletons as the referent group.9 Despite contributing only 2.79% of live births, twins had population-attributable risks for very low birth weight [VLBW], low birth weight [LBW], neonatal, postnatal, and infant deaths of 15.8%, 13.7%, 11.2%, 3.4%, and 8.4%, respectively.

TABLE 2. Relative Risks for Adverse Health Outcomes by Race and Plurality, USA, 1988

LBW = low birth weight; VLBW = very low birth weight.
[Adapted from Luke B, Keith LG: The contribution of singletons, twins and triplets to low birth weight, infant mortality and handicap in the United States. J Reprod Med 37:661, 1992]

The second investigation described mortality rates by gestational age, again using singletons as the referent group and including birth cohorts from 1983 through 1986.10 The 1983 to 1986 fetal death tapes were also used in this analysis. Results are shown in Table 3. Before the publication of these two investigations, comprehensive national data were unavailable. Chorionicity was not considered in either of these two investigations.

TABLE 3. Mortality Rates and RRs [±95% CIs] by Gestational Age and Plurality, USA, 1983-1986
Click here to view Table 3.

Although Figure 2 clearly demonstrates the effect of increasing maternal age on the US multiple birth ratio, no data presently exist for accurate assessment of the direct contribution of reproductive technologies on these changes. Indirect data, biased by admitted self-selection, come from Bleyel at the Triplet Connection.11 As of February 1996, 7064 responses were available to a question on fertility contained in a survey instrument distributed to all expectant parents who requested information from that organization over a 12-year period. The frequency of use of artificially reproductive technology increased from 73.6% among 1863 triplet mother respondents to 92.8% among 600 quadruplet mother respondents to 95.7% among 93 quintuplet mother respondents. Additional data from the population-based East Flanders Prospective Twin Study, reported by Derom and colleagues,12 corroborated these observations. In this registry, not only did the percentage of iatrogenic twins increase from less than 10% in 1976 to more than 50% in 1993, but the frequency of monozygotic splitting after ovulation almost tripled [from 4 to 10 per 1000].13 This latter and as of yet unexplained biologic phenomenon has been confirmed by others who have used in vitro fertilization and embryo transfer technology.14 Although most authors stress differential mortality between multiples and singletons,15 it is equally important to take into account the differential mortality between monochorionic and dichorionic twin pairs. In a recent review of published rates of mortality, Machin [G.M., personal communication] found that the perinatal death rates varied by chorionicity as follows: dichorionic, 11%; monochorionic-diamniotic, 23%; and monochorionic-monoamniotic, 45%. These figures may be high because the data were collated from referral centers. Nonetheless, the pattern of differential mortality is valid.

The preceding paragraphs stress fetal morbidity and mortality, but it is equally important to remember that maternal complications are increased in twin pregnancy. Pregnancy loss and threatened and actual abortions are common. The “vanishing phenomenon” and an arguably higher rate of congenital anomalies are also present. Hydramnios, pregnancy-induced hypertension, antepartum bleeding from abruptio placentae or placenta previa, anemia, and postpartum hemorrhage all are mentioned in classic discussions of the twin condition. As of yet, however, some of these widely recognized concerns have not been refined by any consideration of how the process of “vanishing” might cause bleeding or how the occurrence of twin-to-twin transfusion syndrome [TTTS] might act as an initiating event for the onset of hydramnios. Because operative delivery of twins and other multiples is so prevalent in the United States, the risks inherent to the administration of any anesthetic or operative procedure are also present.

THE CLINICAL CHALLENGE

Previously described clinical challenges for the care of multiples remain valid and are as follows: [1] to enhance early diagnosis of multiple pregnancy, specifically the diagnosis of chorionicity; [2]to institute intensive prenatal, antepartum, and intrapartum care; and [3] to reduce the risk of adverse maternal, fetal, and neonatal outcomes.

These general goals have recently been enhanced by the description of a plan of prenatal care using specific target goals based on risks known to occur at clearly defined gestational stages.15 Such a concept of “tight control” backed up by an extensive educational program is not dissimilar to the concept of tight control for diabetic pregnancies, which has led to a reduction in the rate of stillbirths and macrosomic infants.

In the case of multiples, this new construct of prenatal care is quite simple. Sufficient data currently exist so that a rational plan of prenatal and intrapartum care can be developed and implemented, either in the setting of a special twin clinic or in the office of an individual practitioner. This plan can and should be based on an awareness of the frequency and the timing of potential adverse events and the need for special educational preparation of mothers. Special written materials about twin pregnancy can be prepared and given to parents, along with recommendations for books to read. A similar suggestion has been successful for singleton pregnancies.16

CARE BEFORE 20 WEEKS

Diagnosis

The concept that early diagnosis of twin pregnancy leads to a decreased likelihood of perinatal mortality was described as early as 1979.17 Today, consensus exists that early diagnosis not only decreases mortality and morbidity rates, but is the key to providing optimal antepartum care and the cornerstone of effective management of labor and delivery. Among the most important advantages of early diagnosis is elimination of the possibility that the second twin will remain unrecognized until after the birth of the first. When the senior author [LK] initially reviewed data from the Department of Obstetrics and Gynecology at Northwestern University and the 13 hospitals that then referred their newborns for care from 1970 to 1975, he found that approximately 40% of twin gestations were unknown or undetected either until the mother arrived at the delivery room or until after the delivery of the first twin.18 This figure had declined to 10% by 1984, when Chervenak and co-workers19 published data on a series of 385 consecutive twin deliveries. Recent data from Sweden showed that the majority [97%] of all pregnant women received an ultrasound screen in the year 1990.20 Of these, 90% were performed from 16 to 18 weeks and 10% at 10 to 12 weeks. Thus the likelihood of undiagnosed twins was remote in these circumstances. Population-based figures such as these can be extrapolated to the United States or, for that matter, to any other country.

Whether or not population-based ultrasound should be the standard of care remains a matter of debate. European countries, most notably France and England, consider it as such. In the United States, however, opinions are divided based on whether even a single ultrasound is a cost-effective means to reduce morbidity and mortality. One prospective randomized study suggests that it is not,21 but this opinion is not accepted by all,22 especially when multiples are concerned. Opponents of routine ultrasound suggest that numerous clinical criteria suggestive of multiple pregnancy exist and that one or more should be present to trigger the decision to order an ultrasound. These clinical indicia include: [1] fundal height greater than expected for dates; [2] simultaneous auscultation of two or more fetal heart tones [FHTs] [an attempt to find a second FHT is rarely, if ever, made]; [3] presence of hydramnios; [4] unexplained excessive maternal weight gain; [5] unexpected severe anemia; [6] increased fetal activity; [7] early onset of pregnancy-induced hypertension; [8] personal or family history of twins; and [9] an abnormally elevated alpha-fetoprotein or triple screen in the second trimester. It is important to remember, however, that all of these clinical indicia were well recognized in the era before the advent of ultrasound. Without doubt, their lack of use has contributed to the underdiagnosis of twins.

The use of first-trimester ultrasound for diagnosis of twins is intuitively attractive, but unfortunately not without certain limitations [see later discussion]. In either the first or second trimester, the diagnosis of a twin pregnancy is based on the simultaneous visualization, on the same ultrasound section, of the corresponding body parts of two fetuses.23 Some years ago this observation was mainly restricted to the simultaneous visualization of two fetal heads as they often were the only easily identifiable parts using the technology of the time. In contrast, current technology permits easy identification of complete embryos [Fig. 5]. Ideally both embryos should be visualized at the same initial exploratory examination. However, once a twin gestation has been identified, the examination should continue in order to avoid missing a higher order pregnancy.24 Although multiple sacs are clearly identifiable at 5 weeks of amenorrhea [3 weeks postfertilization], embryonic visualization is usually possible only at week 7 of amenorrhea [depending on operator experience and technical capacity].

In the opinion of most experts, the major advantage of first or very early second trimester diagnosis is the confirmation or adjustment of the estimated date of conception as well as the clear delineation of chorionicity. The confirmation of estimated date of conception is particularly valuable because of the high rate of fetal growth abnormalities in twins as well as higher order multiple pregnancies. It is important to distinguish monochorionic from dichorionic placentas because of the far greater rates of morbidity and mortality for monochorionic compared to dichorionic twins [see earlier discussion]. The question of zygosity is related, but of much less importance. It should be recalled that monozygotic twinning in pregnancies produced via artificially reproductive technology is almost triple the rate seen in spontaneous gestations.13,14 Many of these may be monochorionic. The presence of a webbed, lambda-shaped structure at the end of the interovular membrane is pathognomonic of dichorionic [or multichorionic] pregnancies [Fig. 6].25 This structure is particularly visible between 8 and 13 weeks of amenorrhea, and its presence or absence should be mentioned in any clinical report. The thickness of the intertwin membrane is also indicative of chorionicity. To some degree, the reliability of this measurement is as dependent on the technical conditions of the examination as it is on the actual thickness of the structure being examined [Fig. 7]. The following is a useful clinical tool:

  In the presence of a single placenta, a membrane thickness of 2 mm or less favors the likelihood of monochorionic-diamniotic placentation.
  If, however, the membrane thickness is 4 mm or greater, fused dichorionic-diamniotic placentation is indicated in the presence of a single placental disc.26

In the second trimester, in addition to the detection of the twin condition, advantages of ultrasound examination include reliable estimation of gestational age; exclusion of placenta previa; detection of major structural anomalies, such as spina bifida, acrania, or conjoined twinning; and an opportunity for early bonding between a mother and her children. It is important to remember that later ultrasound is more productive for the detection of structural and/or body stalk abnormalities and progress of growth than for the optimal detection of chorionicity. For this reason, some experts believe that the improved outcomes that accrue from early detection of any deviation from normal more than compensate for the extra cost of multiple ultrasound examinations.22 An extensive review on the use of ultrasound in multiple gestation is provided by Lopez-Zeno and colleagues27 as well as by Bessis.23

As suggested above, clinical methods of diagnosing twin pregnancy are underutilized. More important, each method is fraught with inherent inaccuracies. For example, examination of fundal height is not only dependent on operator experience and skill, but may be reflective of the thickness of the maternal abdominal wall or whether the uterus is in a state of relaxation or contraction at the time of the examination. Because auscultation of the FHT is considered successful once heart tones are found, it is speculative how often this test is used to the point of calling another person to listen for a second sound. Further, unless the onset of hydramnios is acute and severe enough to cause symptoms, the quantity of fluid may be insufficient to allow its detection without the use of an ultrasound scan. Although excessive weight gain may be the first clinical sign of a twin gestation, lack of a precise definition of “excessive” may hinder its clinical utility. Recently the National Academy of Sciences [NAS] recommended an ideal total weight gain of 35 to 45 lb for twin pregnancy,28 but provided no definition of excessive weight gain. The NAS recommendation is useful, however, because it can be the basis of early intervention after initial diagnosis. Indeed, Luke29 and others15 have refined this recommendation to include the necessity of gaining 24 lb by the 24th week. Before recommending a comprehensive plan of weight gain, care givers should take into account the maternal prepregnancy body mass index and stature as well as the fact that about one half of twin pregnancies deliver at the 37th week of gestation or earlier. This latter point mandates an early gain, as opposed to waiting until after 32 weeks to try to augment weight.

Unfortunately, anemia is clearly too ubiquitous a sign to relate solely to multiple gestation. At the minimum, a complete blood count should be obtained and a stool sample studied for the presence of blood and/or parasites if and when severe anemia is present. Because maternal perception of increased fetal activity is uniquely subjective, an ultrasound examination may help determine whether a perception of “too much movement” is indeed a result of twins. The use of a personal or familial history of twins as a screen for obtaining an ultrasound is paradoxical: many women with a strong family history of twinning do not have twins, and many without it do. Of course, such clinical considerations are superfluous in patients who have undergone any form of artificial reproductive technology. In these instances, both the patient and the clinician want to know about the existence of pregnancy and its type as soon as possible. Without ultrasound, their wishes would be frustrated.

Although specific biochemical parameters, such as human chorionic gonadotropin and human placenta lactogen levels, exhibit slow and predictable increases as pregnancy progresses, these cannot be accurately applied to twins.30 This statement may be modified by the recent observation of the use of the three components of the pan - alpha-fetoprotein test.31 In the past, the use of any biochemical marker for the detection of twin pregnancy was hampered by day-to-day fluctuations in individual patients; the possibility of inaccurate conclusions based on miscalculations of gestational age; and the need to confirm any abnormal test with another of greater sensitivity. Because the finding of any abnormal biochemical marker is almost invariably followed by an ultrasound examination, many practitioners [at least at Northwestern] prefer to obtain an ultrasound in the first trimester and biochemical assessments in the second. In contrast, the policy at the University of Michigan is to obtain an ultrasound routinely at 16 to 18 weeks [see earlier discussion]. This may preclude determination of chorionicity to some degree. Regardless, in institutions where first-trimester ultrasound is underutilized, the initial evidence suggesting the presence of twins may be the alpha-fetoprotein test.

Nutritional Considerations

The importance of prenatal nutrition cannot be overstressed. Having said this, until recently it was difficult for practitioners to develop practical guidelines to share with their patients. Although a variety of recommendations on the composition of the prenatal diet have been put forward since antiquity, specific recommendations are of fairly recent origin. Moreover, until 1990, recommendations were based purely on the needs of a singleton pregnancy.

The origins of dietary recommendations in pregnancy until at least the late 1950s were based on the writings of the German obstetrician Prochownik, and his predecessor Glassner, both of whom practiced in the latter half of the 19th century.32,33 Their suggestions were based on the fact that weight restriction was beneficial in producing smaller infants who were more likely to pass through deformed, contracted, rachitic pelves. The Prochownik diet, as well as other forms of weight restriction, which allegedly had no adverse effect on small infants born at term, influenced medical thinking until the middle of the 20th century.32,33 Writers inferred that the fetus and its mother were locked into a parasitic/symbiotic relationship in which the maternal dietary intake or nutritional status was immaterial. These opinions, though vehemently opposed by more physiologically oriented authors, were the basis of the widely accepted recommendation of a total weight gain of 20 lb. This dictum remained unchanged until around the late 1970s, despite the fact that several large hospital series published after 1940 suggested that many patients did not adhere to the 20 lb recommendation and actually gained more [20 to 30 lb] during their pregnancies.32,33 Among the deficiencies of these early hospital studies, however, was a general lack of consideration of preconceptional weight or anthropometric factors, such as short stature and low weight for height [body mass index], along with gestational weight gain as they may have influenced birth weight and length of gestation. After the association between pregravid weight and birth weight was recognized, gestational weight gain began to be viewed as a therapeutic intervention that not only augmented deficiencies of pregravid weight in the mother, but led to increased fetal growth and higher birth weights.32,33

Unfortunately, the “starvation mentality” initiated in the late 1800s was apparent as late as 1980. Taffel34 analyzed the gestational weight gain component of the 1980 National Mortality Survey and the National Fetal Mortality Survey. A total of 23% of women giving birth in 1980 gained less than 21 lb, and 12% less than 16 lb. Black mothers were more likely to gain less than 21 lb and were twice as likely to gain less than 16 lb compared to white mothers. Fortunately, the 1990 NAS publication, Nutrition During Pregnancy, served as a crucial turning point in developing rational guidelines for weight gain in pregnancy.35 This report reviewed all available data on gestational weight gain. It recommended, for the first time, ranges of gain by pregravid weight categories, including 28 to 40 lb for underweight women, 25 to 35 lb for normal-weight women, and 15 to 25 lb for overweight women.28 It also recommended, for the first time, a 35- to 45-lb weight gain in normal women with twin pregnancies.

Two independent studies paralleled the NAS publication and provided an indication of the future direction of subsequent clinical investigations. In one, based on birth/death certificates from the Office of Vital Statistics, Kansas Department of Health and Environment, from the years 1980 to 1996,36 a total of 922 twin gestations delivered at term were described. It was determined that the proportion of infants born with LBW declined as maternal prepregnancy weight status increased. It was further determined that infant birth weights increased linearly with prenatal weight gain for women who entered their pregnancy either underweight or at normal weight, but not for those who were overweight or obese at the start of their pregnancy. In another study, optimal pregnancy outcome [greater than 37 weeks' gestation; both infants greater than 2500 g each, with Apgar scores greater than 7] was associated with gestational weight gains of 44 lb [20 kg] compared to 37 lb [16.8 kg] for women with less-than-optimal outcomes.37

The concept of ideal or optimal twin pregnancy vis-à-vis maternal weight gain was studied extensively by Luke and co-workers38 in a series of papers published between 1991 and 1995. These investigations were based on all twin pregnancies of 28 or more weeks' gestation delivered between January 1, 1979, and December 31, 1989, at the Johns Hopkins Medical Institutions in Baltimore. Pregnancies complicated by extreme maternal obesity or pathologic weight gain were excluded in order to facilitate the evaluation of the maternal anthropometric characteristic of pregravid weight and subsequent gestational weight gain. Of the 274 available pregnancies, 111 were excluded because of one or more exclusion factors, and 163 twin pairs remained for analysis. When total weight gain was investigated in terms of early [before 24 weeks] and late [after 24 weeks] gain, twins with higher birth weights and shorter lengths of stay were delivered of mothers with higher late rates of gain. Luke and colleagues39 suggested that an early rate of gain of 1 lb/week before the 24th week and a late rate of gain of 1.5 lb per week might have therapeutic advantage. These analyses support the recommendations of the National Academy of Sciences. More important, however, they clarify the relationship between early and late rate of weight gain, total weight gain, and perinatal outcomes, including birth weight and length of stay [LOS], as shown in Table 4.

TABLE 4. Comparison of Perinatal Outcomes by Term vs Preterm and by Average of Twin Birth Rates