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9 Weight Gain in Twin Pregnancies loin pregnancies are excluded from most pregnancy studies. A1- though some reports give infant weights for large numbers of twin births, few provide data on maternal weight gain, body composition changes, or postpartum weight loss. A better understanding of twin pregnancies could be of major public health importance. In the United States in 1986, less than 2% of all births were twin births, but 1656 of the low-birth-weight infants were twins (NCHS, 1988~; infant mortality is also correspondingly higher in twin births. Figure 9-1 illustrates the continuing high incidence of low birth weight and very low birth weight among twins. Weight gain in a twin pregnancy is expected to exceed weight gain in a single-fetus pregnancy because of greater increases in both maternal tissues and intrauterine weight. Selection of twin pregnancies to identify the appropriate weight gain or the normal or optimal course poses a number of problems, in addition to those encountered in studying singleton pregnancies, specifically: More mothers of twins may have taken action to restrict their weight gain, especially if they do not know until late in gestation that they are pregnant with twins. · Many twin infants have low birth weights, even at full-term. · Outcomes may differ for mixed-sex twin pairs in comparison with those for same-sex pairs. · Many twin deliveries are preterm. 212
WEIGHT GAIN IN TWIN PREGNANCIES 70 `~5 50 c' o - s .= ,_ ·t ~30 m ~ , ._ 0 ~ - . - ~ ~ 20 a) > ~ ,> 3 0 ~ _1 ~0 - o 0- 15 213 Black (< 2,500 9) (60.4%) (58.7%) (61.4%) (61.5%) (51.4%) (52.6%) (13.6%) (1 3.0%) - - ~ _ ~ (48.4%) (47.2%) White (< 2,500 9) Black (< 1,500 9) (1 5.9%) (1 6.3%) it_ White (< 1,500 9) (9.2%) (8.8%) (8.8%) 8 1 960 1 970 Year 1980 1 985 FIGURE 9-1 mends in low and very low birth weight of live-born twins in the United States from 1960 through 1985. Based on unpublished data from the National Vital Statistics System, computed by the Division of Analysis from data compiled by the Division of Vital Statistics, National Center for Health Statistics. . Elective cesarean delivery and labor induction before 40 weeks of gestation are more common for women carrying twins. · Certain complications (e.g., preeclampsia and anemia) are more common for women carrying twins. . Outcomes may differ for monozygotic and dizygotic twins. Standards for identifying a normal twin pregnancy have not yet been established. Some studies indicate that approximately one-third of twin births occur before 37 weeks of gestation (Ho and Wu, 1975) and that the mean gestational age at delivery is near 37 weeks (see Tables 9-lA and 9-lB). Longer gestations, with the resultant higher birth weights and lower mortalities, might be achievable if more could be learned about the physiology and progress of optimal twin pregnancies. Although the birth weights of twins start to fall below the weights of similar-aged infants at about 30 weeks of gestation, it is arguable whether this difference should be accepted as inevitable. If twins have not yet been identified during prenatal care, high maternal weight gain (especially early in pregnancy) may lead to self-imposed food restriction or may stimulate warnings from the health care provider for the woman to curb her food intake. If twins are expected, concern about hypertension (more frequent in women with twin pregnancies) may also
214 NUTRITIONAL STATUS AND WEIGHT GAIN TABLE 9-lA Mean Birth Weights of Twins of Both Genders Combined Location of Study and Reference New Haven, Conn., USA Yarkoni et al., 1987 Chicago, Ill., USA 488 Keith et al., 1980 Sweden Grennert et al., 1978 Number of Twin Pairs Stage of Mean Birth Weights, g + SDa Gestation at -~ Birth, wk Twin 1 Twin 2 Both Twins NRb 35 37.5 NR 153 NR 2,673 + 582 2,388 + 742 2,s4oc 2,614 + 490 2,314 + 766 2,470C NR NR Holland239 37.4 NR NR 2,388 + 576 Hofman, 1984 Finland10 36.8 2,720 2,743 Lammintausta and + 310d + 332d Erkkola, 1979 Africa1,000 NR 2,385C 2~349C 2,367C Farrell, 1964 a SD = Standard deviation. b NR = Not reported. c Standard deviation was not reported. d Standard deviation was derived from the reported data. TABLE 9-lB Mean Birth Weight of Twins, by Gender and Zygosity When Known Birth Weight + SDa by Gender and Zygosity Males Females Reference and Location of Study Dizygotic Monozygotic Dizygotic Monozygotic Corney et al., 1981 2,728 + 516, 2,595 + 684, 2,601 + 490, 2,385 + 607, Oxford, United Nb - 160 N = 36 N = 144 N = 18 Kingdom Aberdeen, United 2,542 + 591, 2,439 + 528, 2,557 + 516, 2,428 + 463, Kingdom N= 110 N= 56 N= 112 N= 48 Pilic et al., 1985 2,455 + 704,~ 2,316 + 651,C Belgrad, Yugoslavia N = 360 N = 360 a SD = Standard deviation. b N = sample size. c Zygosity not specified.
WEIGHT GAIN IN IRON PREGNANCIES 215 result in some degree of dietary control. Current data do not address these issues and their possible contribution to observed outcomes. In the following sections, data on pregnancy outcome are reviewed along with information on maternal factors that might influence pregnancy outcome. MORTALITY The high mortality tales of twins appear to be influenced by the preponderance of low-weight, early births. In England and Wales in 1983, twins represented 2% of all births but 9% of perinatal deaths (Bolting et al., 1987~. Declining twin mortality rates over time have been documented in several studies (De Muylder et al., 1982; van der Pot et al., 1982~. A decrease in the proportion of low-birth-weight twins would have a very large effect on mortality. However, since preterm delivery leads to a substantial proportion of the lower mean birth weight of twins, effective interventions may be dependent on improved understanding of the factors that contribute to early labor. BIRTH WEIGHT Table 9-lA and 9-lB include data on twin birth weights from several studies, more than half of which were conducted outside of the United States. In twin pregnancies, as in singleton pregnancies, birth weight is lower in female infants, infants born to primiparous women (van der Pot et al., 1982), and infants of smokers (Luke, 1987), as well as in the second twin. The data indicate that twin mean birth weight is as much as 700 g lower than the singleton birth weight and that gestation is about 2 to 3 weeks shorter. As in singleton pregnancies, it has also been shown that light-for-date twins have lower weight placentas than those of appropriate- for-date twins (Tayama et al., 1983~. GESTATION LENGTH AND LOW BIRTH WEIGHT The mean gestation length for twins is between 37 and 38 weeks (gables 9-lA and RIB). Preterm delivery rates of 42.2% have been reported in Canada (De Muylder et al., 1982~. Low-birth-weight rates were higher in live-born white twins in the United States during a similar period, specifically, 51.4% in 1960 declining to 47.2~o in 1985 (J. Kleinman, National Center for Health Statistics, personal communication, 1989~. IF et al. (1983) examined twin and single fetuses that were aborted 8.5 to 21 weeks after the last menstrual period and concluded that twin fetuses may be about 6 days younger than would ordinarily be estimated from the date of the last menstrual period. This conclusion would be consistent with
216 NUTRITIONAL STATUS AND WEIGHT GAIN the smaller head size noted in twins throughout gestation, but means that they are even younger at delivery than their generally early delivery date indicates. MATERNAL FACTORS Physical Characteristics and Weight Gain In one observational study, Konwinski et al. (1974) noted that none of the five women weighing over 65 kg (143 lb) before pregnancy delivered at or before 37 weeks of gestation, whereas 15 of the 22 women weighing less than 65 kg (143 lb) delivered early. No such relationship was found between length of gestation and insufficient pregnancy weight gain (categorized as <6 kg, or 13 lb, at 28 weeks, <7 kg, or 15 lb, at 32 weeks; and <8 kg, or ~18 lb, at 36 weeks of gestation). However, a statistically significant increase in preterm delivery was observed in those twin gestations in which the mother lost 1 kg or more between weeks 32 and 36 of gestation. More recently, Luke (1987) has related low early weight gain to preterm delivery of twins. In an observational, prospective study of 132 twin pregnancies, Houlton et al. (1981) have shown that obese mothers have a reduced risk for one or both twins to be growth retarded. They also identified a maternal height of less than 156 cm (~61 in.) and a weight loss or stable weight over three consecutive prenatal visits as factors that were predictive of twins at risk for growth retardation. Weight gains in twin pregnancies have been reported in a few studies. In Finland, Lammintausta and Erkkola (1979) observed that maternal weight gain through 30 to 33 weeks of gestation was 11.4 ~ 1.6 kg (25 ~ 3.5 lb; mean ~ standard deviation). If weight gain had continued at the same rate until 37 weeks of gestation, from 13 to 14 kg (29 to 31 lb) would have been gained. Schneider et al. (1978) distinguished weight gain by zygosity in a prospective study of 86 twin pregnancies. By week 36 of gestation, mothers of monozygotic twins had gained 12.25 kg ~ 4.27SD (27.0 ~ 9.4 lb) and mothers of dizygotic twins had gained 13.86 ~ 4.18 kg (30.5 ~ 9.2 lb) (not significantly different). An earlier study in France also showed higher weight gains at 28 weeks of gestation by mothers of dizygotic twins (Konw~nski et al., 1974) (see 1bble 9-2~. Using data from earlier studies, Campbell (1986) reported a mean weight gain of 14.6 kg (32.1 lb) at 36 weeks of gestation in twin pregnancies and a mean gain of 11.1 kg (24.4 lb) in the same period in singleton pregnancies (standard deviation and number of participants were not given; Bible 9-3~. The reported difference in weight gain barely accounted for the difference that would be expected from the weight of the additional fetus
WEIGHT GAIN IN TWIN PREGNANCIES TABLE 9-2 Weight Gain in Women Bearing Monozygotic or Dizygotic Twins 217 Reference and Study Population Size Mean Maternal Weight Gain + SD,a kg, by Type of Twin Pregnancy Length of Gestation, wk Monozygotic Dizygotic Schneider et al., 1978; 28 8.89 + 3.43b 10.18 + 3.13b monozygotic: N = 40; 32 10.95 + 3.84b 10.95 + 3.46b dizygotic: N = 46 36 12.25 + 4.27b 13.86 + 4.18b Konwinski et al., 1974 28 7.3 + 1.7c 8.3 + 1.5c (population size not reported) a SD = Standard deviation. b Standard deviation was erroneously reported as standard error. c It was not stated whether this variance represented standard deviation or standard error. TABLE 9-3 Weight Gain in Twin and Singleton Pregnanciesa Period of Gestation, wk Weight Gain, kg/wk, by Type of Pregnancyb Single 0.42 0.47 0.40 Twin 1~20 2(}30 3(}36 0.60 0.54 0.64 ~36 11.1 kg total gain 14.6 kg total gain a From Campbell (1986) with permission. b Standard deviations not given. and placenta and thus does not indicate additional weight increases in the body of the twin-bearing mother. Three studies, two of which were reported as abstracts, have provided more current data. Luke (1987) found a rate of weight gain in twin preg- nancies of nonsmokers (Table 9-4) that was higher than the rate reported by Campbell (1986; Table 9-3), but the rate for smokers was not. The data in Table 9-4 indicate that a lower rate of early weight gain may contribute to early delivery in both smokers and nonsmokers. Their data also show that smokers have lower-weight infants at term (2,478 g) than do nonsmokers (2,692 g). Brown and Schloesser (1989) studied the birth records of nearly 2,000 twins born in Kansas from 1980 to 1986. They found that birth weight increased with increasing maternal weight gain (not controlled for length
218 NUTRITIONAL STATUS AND WEIGHT GAIN TABLE 9-4 Weight Gain During Twin Gestations in Smokers and Nonsmokersa Period of Gestation, wk Weight Gain, k~/wk, by Maternal Smoking Status Nonsmokers Smokers O to 30 0.72 0.60 30 to birth, preterm 0.57 0.50 30 to birth, at full term 0.88 0.65 O to 38 13 kg total gain 10.5 kg total gain a Based on Luke (1987~. b Standard deviations not given. Of gestation). The rate of low birth weight ranged from a high of 32.3% in underweight women to 20.0% in very obese women, based on maternal prepregnancy weight for height. The lowest perinatal mortality occurred in the 3,000- to 3,500-g birth-weight group. For this group, maternal weight gain was 20.1 kg (44.2 lb) for underweight women, 18.6 kg (40.9 lb) for normal-weight women, and 13.3 kg (29.2 lb) for very obese women. A retrospective medical records study of 217 twin pregnancies of women over age 18 delivering in Seattle, Washington, indicated that unre- stricted weight gain (from prepregnancy to within 1 week of delivery) was 18.5 kg (40.6 lb) (Pederson et al., 1989~. The prepregnancy weight averaged 63.2 kg (139.6 lb). Weight gain averaged 20 kg (44 lb) for those mothers who gave birth at term to two live-born infants weighing at least 2,500 g and with 5-minute Apgar scores of at least 7, termed "optimal outcome." Mothers with a "less than optimal outcome" had gained 16.8 kg (37 lb). (For the entire group, the mean birth weight was 2,602 ~ 586.6 g and the mean gestational age was 36.9 ~ 3.2 weeks.) Data from the 1980 National Natality Survey for 124 white, non- Hispanic, married mothers carrying twins are shown in Table 9-5. On average, mothers of twins gained approximately 2 to 4 kg (4 to 9 lb) more than did mothers of single infants. Adjustment for increased placental weight in twin pregnancies changes these figures only slightly. The data in Table 9-5 provide evidence that mothers of twins in the United States gain more per week than do those who have single births. In general, the study results are consistent in that they show a rela- tionship of weight gain to birth weight and low-birth-weight rates in twin as well as in singleton pregnancies. A relationship of weight gain to duration is less uniformly reported. Weight gains in twin pregnancies with good birth weight outcomes are substantially higher than they are in singleton pregnancies, averaging about 22 kg (44 lb).
WEIGHT GAIN IN TWIN PREGNANCIES 219 TABLE 9-5 Comparison of Full-Term Total Weight Gain and Net Gain per Week for Women Delivering Single and Twin Births, by Body Mass Index (BMI)a Maternal Weight Gain, kg, by Type of Birth (aIld Sample Size) Single Twin Total Total Weight Net Weight Gain Weight Net Weight Gain BMI Category Gain, kg per Week, kgb Gain, kg per Week, kg Low (<19.8) 13.6 0.27 18.2 0.37 (N= 1,027) (N= 31) Moderate (19.~26.0) 13.8 0.26 17.7 0.37 (N= 2,393) (N= 62) High (~26.0) 12.4 0.21 14.1 0.25 (N= 526) (N= 31) a Unpublished data based on the 1980 National Natality Survey. b Net weight gain per week is calculated by subtracting the weight of the baby from the total gestational weight gain before computing the weekly gain. Body Composition It is not clear from body composition studies of twin pregnancies whether the additional maternal weight gain is composed of maternal fat or lean tissue. Internal contradictions in reported studies (Campbell, 1983, 1986; Campbell and MacGillivray, 1977) suggest that they are unreliable and do not warrant discussion. Further study is clearly needed. Physiologic Adaptations Romney et al. (1955) found that uterine circulation in one twin ges- tation was double the average value observed in a set of five singleton pregnancies. It is of interest that this twin pregnancy was a full-term pregnancy the two infants weighed 3.3 and 3.6 kg. Adequate uterine circulation may be critical to maintaining the growth of the twins late in pregnancy. In another study, calcium balance remained positive in a woman preg- nant with twins, largely because of a marked reduction in urinary calcium excretion (Duggin et al., 1974~. Several studies demonstrated that levels of many of the major pregnancy hormones are higher in twin pregnancies than they are in singleton pregnancies (e.g., Knight et al., 1981; MacGillivray, 1978; Tayama et al., 1983~. These hormones could contribute to augment- ing pregnancy adjustments, increasing weight gain (Schneider et al., 1978), and altering maternal body composition.
220 NUTRITIONAL STATUS AND WEIGHT GAIN SUMMARY The literature suggests that in twin pregnancies weight gain is higher than the weight accounted for by the mass of the additional conceptus. Data on the association of twin weight with mortality indicate that birth weights that are similar to those of singleton births, and that are much higher than the usual birth weights of twins, are associated with minimum perinatal mortality. As in singleton pregnancies, twin birth weight appears to be related to maternal weight gain and inversely related to maternal smoking. Evidence suggests that maternal weight gain in a twin pregnancy is related to both the length of gestation and the percentage of infants born with a low birth weight. Since information on body composition is incomplete and unreliable, it is not possible to draw conclusions about the components of the additional weight gain. Limited information suggests that physiologic and metabolic adaptations are greater during twin pregnancies than they are in singleton pregnancies. This information is consistent with observations on weight gain but is insufficient to provide a definitive statement about which changes are necessary for a successful twin pregnancy. CLINICAL IMPLICATIONS lUtal weight gain of 16 to 20.5 kg (35 to 45 lb) Is consistent with a favorable outcome of a full-term twin pregnancy. This suggests that a woman who Is pregnant with twins should aim for a weekly weight gain of approximately 0.75 kg (1.5 lb) during the second and third trimesters of pregnancy. REFERENCES Botting, B.J., I.M. Davies, and ~J. MacFarlane. 1987. Recent trends in the multiple births and associated mortality. Arch. Dis. Child. 62:941-950. Brown, J.E., and P. Schloesser. 1989. Prepregnancy weight status, prenatal weight gain, birth weight, and perinatal mortality relationships in term, twin pregnancies. FASEB J. 3:A648. Campbell, D.M. 1983. Dietary restriction in obesity and its effect on neonatal outcome. Pp. 243-250 in D.M. Campbell and M.D.G. Gillmer, eds. Nutrition in Pregnancy: Proceedings of the Tenth Study Group in the Royal College of Obstetricians and Gy- naecologists, September, 1982. The Royal College of Obstetricians and Gynaecologists, London. Campbell, D.M. 1986. Maternal adaptation in twin pregnancy. Semin. Perinatol. 10:14-18. Campbell, D.M., and I. MacGillivray. 1977. Maternal physiological responses and birth- weight in singleton and twin pregnancies by parity. Eur. J. Obstet., Gynecol. Reprod Biol. 7:17-24. Corn ey, G., D. Seedburgh, B. Thompson, D.M. Campbell, I. MacGillivray, and D. Timlin. 1981. Multiple and singleton pregnancy: differences between mothers as well as offspring. Prog. Clin. Biol. Res. 69~107-114. incidence of
WEIGHT GAIN IN TWIN PREGNANCIES 221 De Muylder, X, J.M. Moutquin, M.F. Desgranges, B. Leduc, and F. T~7~ro-Lopez. 1982. Obstetrical profile of twin pregnancies: a retrospective review of 11 years (1969-1979) at Hospital Notre-Dame, Montreal, Canada. Acta. Genet. Med. Gemellol. 31:149-155. Duggin, G.G., N.E. Dale, R.C Lyneham, R.A. Evans, and DJ. Tiller. 1974. Calcium balance in pregnancy. Lancet 2:926-927. Farrell, NG.W. 1964. Din pregnancy: a study of 1,000 cases. S. Afr. J. Obstet. Gynaecol. 2:35-41. Grennert, L^, P.H. Persson, and G. Gennser. 1978. Intrauterine growth of twins judged by BED measurements. Acta Obstet. Gynecol. Scand., Suppl. 78:28-32. Ho, S.K, and P.Y.K Wu. 1975. Perinatal factors and neonatal morbidity in twin pregnancy. Am. J. Obstet. Gynecol. 122:979-987. HoEman, M.A. 1984. Energy metabolism and relative brain size in human neonates from single and multiple gestations: an allometric study. Biol. Neonate 45:157-164. Houlton, M.C.C., M. Marivate, and R.H. Philpott. 1981. The prediction of fetal growth retardation in twin pregnancy. Br. J. Obstet. Gynaecol. 88:264-273. Icy, L., M.A. Lavenhar, A. Jakobovits, and H.A. Kaminetzky. 1983. The rate of early intrauterine growth in twin gestation. Am. J. Obstet. Gynecol. 146:970-972. Keith, L., R. Ellis, G.S. Berger, and R. Depp. 1980. The Northwestern University Multihospital loin Study. I. A description of 588 twin pregnancies and associated pregnancy loss, 1971 to 1975. Am. J. Obstet. Gynecol. 138:781-789. Knight, G.J., E.M. Kloza, D.E. Smith, and J.E. Haddow. 1981. Efficiency of human placental lactogen and alpha-fetoprotein measurement in twin pregnancy detection. Am. J. Obstet. Gynecol. 141:585-586. Konwinski, T., C. Gerard, A.M. Hult, and E. Papiernik-Berkhauer. 1974. Maternal pregestational weight and multiple pregnancy duration. Acta Genet. Med. Gemollol., Suppl. 22:44-47. Lammintausta, R., and R. Erkkola. 1979. Effect of long-term salbutamol treatment on renin-aldosterone system in twin pregnancy. Acta Obstet. Gynecol. Scand. 58:447-451. Luke, B. 1987. Twin births: influence of maternal weight on intrauterine growth and prematurity. Fed. Proc., Fed. Am. Soc. Exp. Biol. 46:1015. MacGillivray, I. 1978. Twin pregnancies. Obstet. Gynecol. Annul 7:135-151. NCHS (National Center for Health Statistics). 1988. Vital Statistics of the United States, 1986. Vol. I-Natality. DHHS Publ. No. (PHS) 88-1123. National Center for Health Statistics, Public Health Service, U.S. Department of Health and Human Services, Hyattsville, Md. 454 pp. Pederson, A.L., B. Worthington-Roberts, and D.E. Hickok. 1989. Weight gain patterns during twin gestation. J. Am. Diet. Assoc. 89:642-646. Pilic, Z., V. Sulovic, S. Markovic, R. Radosevic, and V. Kesic. 1985. Genetic factom and fetal growth sex constitution and birthweight in twins. Int. J. Gynaecol. Obstet. 23:421-425. Romney, S.L., D.E. Reid, J. Metcalfe, and C.S. Burwell. 1955. Oxygen utilization by the human fetus in utero. Am. J. Obstet. Gynecol. 70:791-799. Schneider, L., M. Rigaud, J.L. Tabaste, P. Chebroux, B. Lacour, and J. Baudet. 1978. HPL measurements: relationships with materT~al weight gain in twin pregnancy. Prog. Clin. Biol. Res. 24C:123-128. Tayama, C., S. Ichimaru, M. Ito, M. Nakayana, M. Maeyama, and I. Miyakawa. 1983. Unconjugated estradiol, estriol and total estriol in maternal peripheral vein, cord vein, and cord arte~y serum at delive~y in pregnancies with intrauterine growth retardation. Endocrinol. Jpn. 30:155-162. van der Pol, J.G., O.P. Bleker, and P.E. Treffers. 1982. Clinical bedrest in twin pregnancies. Eur. J. Obstet., Gynecol. Reprod. Biol. 14:75-80. Yarkoni, S., E.^ Reece, T. Holford, T.Z. O'Connor, and J.C Hobbins. 1987. Estimated fetal weight in the evaluation of growth in twin gestations: a prospective longitudinal study. Obstet. Gynecol. 69:636-639.