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OCR for page 212
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
OCR for page 213
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 Based on unpublished data from the National Vital Statistics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
OCR for page 214
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.
OCR for page 215
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
OCR for page 216
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
OCR for page 217
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
OCR for page 218
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).
OCR for page 219
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.
OCR for page 220
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.
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incidence of
OCR for page 221
WEIGHT GAIN IN TWIN PREGNANCIES
221
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Representative terms from entire chapter:
twin pregnancies
