Maternal anthropometry and pregnancy outcome among Jerusalem women

Accuracy of a mixed effects model interpolation technique for the estimation of pregnancy weight values

BACKGROUND

Interpolation of missing weight values is sometimes used in studies of gestational weight gain, but the accuracy of these methods has not been established. Our objective was to assess the accuracy of estimated weight values obtained by interpolating from the nearest observed weight values and by linear and spline regression models when compared with measured weight values.

METHODS

The study population included participants enrolled in the LIFECODES cohort at Brigham and Women's Hospital. We estimated weights at 28 (n=764) and 40 (n=382) weeks of gestation using participants' two nearest observed weights and subject-specific slopes and intercepts derived from repeated measures mixed effects models. In separate models, gestational age was parameterised as a linear and restricted cubic spline variable. Mean differences, absolute error measures and correlation coefficients comparing observed and estimated weights were calculated.

RESULTS

Mean differences and mean absolute error for weights derived from the 28-week linear model (0.18 lbs (SD 6.92), 2.73 lbs (SD 6.35)) and 40-week linear model (-0.40 lbs (SD 5.43) and 2.84 lbs (SD 4.65)) were low. Mean differences were somewhat greater at 28 weeks for weight values derived from the nearest two observed values (mean difference -1.97 lbs (SD 8.74)) and from spline models (mean difference -2.25 lbs (SD 7.13)). Results were similar at 40 weeks.

CONCLUSIONS

Overall, weight values estimated using this interpolation approach showed good agreement with observed values. When repeated measures of weight are available, mixed effects models may be used to interpolate of missing weight values with minimal error.

Patterns and trajectories of gestational weight gain: a prospective cohort study

BACKGROUND

Gestational weight gain in excess of or below Health Canada's guidelines is known to increase the risk of adverse outcomes for both the woman and her baby. This study describes patterns and trajectories of total and rate of gestational weight gain in a large prospective cohort of pregnant women and adolescents in the Alberta Pregnancy Outcomes and Nutrition study.

METHODS

We collected weight and height data for 1541 pregnant adolescents and women (mean age 31 years, < 27 weeks' gestation) recruited through advertisements and physicians' offices in Calgary and Edmonton between May 2009 and November 2012. Data were collected once during each trimester following enrolment and once at about 3 months post partum. The participants were categorized according to their prepregnancy body mass index (BMI) as underweight, of normal weight, overweight or obese. We calculated distributions of total and weekly rates of weight gain and determined trajectories of weight gain for each prepregnancy BMI category.

RESULTS

Of the 1541 participants, 761 (49.4%) exceeded Health Canada's guidelines for total gestational weight gain, and 272 (17.6%) gained less weight than recommended. A total of 63 (19.2%) and 38 (23.6%) participants categorized as overweight or obese, respectively, exceeded the recommended upper limit by 5 to less than 10 kg, and 53 (16.2%) and 27 (16.8%), respectively, exceeded the upper limit by at least 10 kg. Ninety-five participants (30.3%) in the overweight group and 59 (39.6%) of those in the obese group gained weight at more than double the recommended rate between the second and third trimesters. The median weight gain for participants in the normal, overweight and obese categories had exceeded recommended upper limits by about 30, 20 and 18 weeks' gestation, respectively.

INTERPRETATION

Adherence to Health Canada's guidelines for gestational weight gain was low. Excess gestational weight gain was most marked among those with a prepregnancy BMI in the overweight or obese category. The findings suggest that weight management in pregnancy is challenging and complex. Messages and supports that are tailored for women in different prepregnancy BMI categories may help to improve guideline-concordant gestational weight gain.

Sex differences in fetal growth responses to maternal height and weight

Sex differences in fetal growth have been reported, but how this happens remains to be described. It is unknown if fetal growth rates, a reflection of genetic and environmental factors, express sexually dimorphic sensitivity to the mother herself. This analysis investigated homogeneity of male and female growth responses to maternal height and weight. The study sample included 3,495 uncomplicated singleton pregnancies followed longitudinally. Analytic models regressed fetal and neonatal weight on tertiles of maternal height and weight, and modification by sex was investigated (n = 1,814 males, n = 1,681 females) with birth gestational age, maternal parity, and smoking as covariates. Sex modified the effects of maternal height and weight on fetal growth rates and birth weight. Among boys, tallest maternal height influenced fetal weight growth before 18 gestational weeks of age (P = 0.006), and prepregnancy maternal weight and body mass index subsequently had influence (P < 0.001); this was not found among girls. Additionally, interaction terms between sex, maternal height, and maternal weight identified that males were more sensitive to maternal weight among shorter mothers (P = 0.003) and more responsive to maternal height among lighter mothers (P < or = 0.03), compared to females. Likewise, neonatal birth weight dimorphism varied by maternal phenotype. A male advantage of 60 g occurred among neonates of the shortest and lightest mothers (P = 0.08), compared to 150 and 191 g among short and heavy mothers, and tall and light-weight mothers, respectively (P = 0.01). Sex differences in response to maternal size are under-appreciated sources of variation in fetal growth studies and may reflect differential growth strategies.

How should gestational weight gain be assessed? A comparison of existing methods and a novel method, area under the weight gain curve

BACKGROUND

Gestational weight gain is important to assess for epidemiological and public health purposes: it is correlated with infant growth and may be related to maternal outcomes such as reproductive health and chronic disease risk. Methods commonly used to assess weight gain incorporate assumptions that are usually not borne out, such as a linear weight gain, or do not account for differential length of gestation.

METHODS

We introduce a novel method to assess gestational weight gain, the area under the weight gain curve. This is easily interpretable as the additional pound-days carried due to pregnancy and avoids many flaws in alternative assessments. We compare the performance of the simple difference, weekly gain, Institute of Medicine categories and the area under the weight gain curve in predicting birthweight and maternal weight retention at 6, 12, 24 and 36 months postpartum. The analytic sample comprises 2016 participants in Project Viva, an observational prospective cohort study of pregnant women in Massachusetts.

RESULTS

For birthweight outcomes, none of the weight gain measures is a meaningfully superior predictor. For 6-month postpartum weight retention the simple difference is superior, while for 12-, 24- and 36-month weight retention the area under the weight gain curve is superior.

CONCLUSIONS

These findings are plausible biologically: the same amount of weight gained early vs later in the pregnancy may reflect increased maternal fat stores. The timing of weight gain is reflected best in the area under the weight gain curve. Different methods of measuring gestational weight gain may be appropriate depending on the context.

Weight loss during pregnancy is associated with adverse pregnancy outcomes among HIV-1 infected women

In a prospective study of 1002 pregnant, HIV-1 infected Tanzanian women, we examined the incidence of fetal death, preterm delivery, low birth weight (LBW), and small for gestational age (SGA) births in relation to maternal anthropometry at the first prenatal visit, weight loss, and low weight gain during pregnancy. Anthropometric measurements were obtained monthly during the 2nd and 3rd trimesters. Low maternal height and weight at the first visit were significantly related to lower mean birth weight and increased risk of SGA, but not to preterm delivery. Maternal stature < 150 cm was significantly related to fetal death. Weight loss during pregnancy, defined as a negative slope of the regression of weight measurements on the week of gestation, occurred in 10% of the women. It was related to increased relative risk (RR) of fetal death (RR = 1.83, 95% CI = 0.93, 3.57), preterm delivery (RR = 1.85, 95% CI = 1.40, 2.44), and LBW (RR = 2.85, 95% CI = 1.69, 4.79) after adjusting for multivitamin supplementation, height, primiparity, baseline weight, malaria, CD4 cell count, HIV disease stage, and intestinal parasitoses. The significant association with fetal death was stronger for weight loss during the 2nd trimester, whereas increased risks of preterm delivery and LBW were higher for weight loss during the 3rd. Similar but weaker associations were found with low weight gain during pregnancy (slope < 25th percentile). We conclude that poor anthropometric status at the first prenatal visit and weight loss during pregnancy among HIV-1 infected women are strong risk factors for adverse pregnancy outcomes.

Height of young men

We analysed the height of young men in Belgium, using 613 257 records of medical examinations made prior to their conscription into the army (about 68% of the male population concerned). All analyses showed very significant associations. Height differed according to the region (-1.24cm in Wallonia, French-speaking and poorer) compared to Flanders (Dutch-speaking and richer), when "age-class" and year are taken into account. The smallest men lived in Hainaut (a deprived area), the tallest ones in Walloon Brabant (wealthy green suburbs of the capital). Height increased across time (+1.11cm, 1978-1990) and with "age-class" (+2.66cm, 18-26years), controlling for other factors. The increase in Brussels stops in 1983, probably due to other socio-demographic evolutions.

Pattern and predictors of weight gain during pregnancy among HIV-1-infected women from Tanzania

Progression of HIV disease is often accompanied by weight loss and wasting. Gestational weight gain is a strong determinant of maternal and neonatal outcomes; however, the pattern and predictors of weight gain during pregnancy among HIV-positive women are unknown. We obtained monthly anthropometric measurements in a cohort of 957 pregnant women from Tanzania who were HIV infected. We estimated the weekly rate of weight gain at various points during the second and third trimesters of pregnancy and computed rate differences between levels of sociodemographic, nutritional, immunologic, and parasitic variables at the first prenatal visit. The change in mid-upper arm circumference (MUAC) from baseline to delivery was also examined. The rate of weight gain decreased progressively during pregnancy. There was an average decline of 1 cm in MUAC between weeks 12 and 38. Lower level of education and helminthic infections at first visit were associated with decreased adjusted rates of weight gain during the third trimester. High baseline MUAC, not contributing to household income, lower serum retinol and selenium concentrations, advanced clinical stage of HIV disease, and malaria infection were related to decreased rates of weight gain during the second trimester. Low baseline CD4 T-cell counts were related to a poorer pattern of weight gain throughout pregnancy. Prevention and treatment of parasitic infections and improvement of nutritional status are likely to enhance the pattern of gestational weight gain among HIV-infected women.

Effect of multivitamin and vitamin A supplements on weight gain during pregnancy among HIV-1-infected women

BACKGROUND

The pattern of weight gain during pregnancy among HIV-infected women is largely unknown. Multivitamin supplementation was shown to be effective in preventing adverse pregnancy outcomes among HIV-positive women. These protective effects could be mediated in part by an improvement in the pattern of gestational weight gain.

OBJECTIVE

We examined the effects of multivitamin and vitamin A supplements on weight gain during the second and third trimesters of pregnancy among HIV-infected women.

DESIGN

We enrolled 1075 pregnant, HIV-1-positive women from Dar es Salaam, Tanzania, in a randomized, placebo-controlled trial. Using a 2-by-2 factorial design, we assigned each woman to 1 of 4 regimens: multivitamins (thiamine, riboflavin, niacin, folic acid, and vitamins B-6, B-12, C, and E), vitamin A, multivitamins including vitamin A, or placebo. The women took these oral supplements daily and were weighed monthly until the end of pregnancy.

RESULTS

The mean rate of weight gain was 306 g/wk during the second trimester and 247 g/wk during the third trimester. During the third trimester, average weight gain was significantly greater (by 304 g; 95% CI: 17, 590; P = 0.04) and the risk of low rate of weight gain (<or= 100 g/wk) was significantly lower (relative risk: 0.73; 95% CI: 0.58, 0.93) in women who received multivitamins than in women who did not. Multivitamins including vitamin A were protective against low weight gain during the second trimester compared with multivitamins alone.

CONCLUSION

Multivitamin supplementation during pregnancy improves the pattern of weight gain among HIV-infected women.

HIV status and sociodemographic correlates of maternal body size and wasting during pregnancy

OBJECTIVE

To examine HIV status and sociodemographic variables as correlates of body size (height, body mass index (BMI), and mid-upper-arm circumference (MUAC)) and wasting (MUAC <22 cm) in pregnant women.

DESIGN

Cross-sectional study.

SETTING

Four antenatal clinics in Dar es Salaam, Tanzania.

SUBJECTS

Women presenting for first prenatal visit before the 23rd week of gestation, between April 1995 and July 1997 (n=13 760).

RESULTS

Mean MUAC, BMI and height were 25.5 cm, 23.5 kg/m(2) and 155.1 cm, respectively. The prevalence of HIV infection was 13.1% and the overall prevalence of wasting was 4.7%. Wasting was 34% (95% CI=3%, 73%) more prevalent among HIV-infected than in uninfected mothers, after adjusting for week of gestation, height and sociodemographic indicators. The risk of wasting associated with HIV infection was highest among women with low level of education or unable to contribute to the household income. From a multiple linear regression model, BMI was positively associated with mother's age, level of education and money spent on food, but not with HIV infection, after adjusting for week of gestation. In multivariate analysis, height increased monotonically by categories of maternal age and level of education, and was also positively correlated with the ability to contribute to household income, the amount of money spent on food per person per day, and having a professional partner.

CONCLUSION

HIV infection is a significant risk factor for wasting among pregnant women, particularly in groups of low socioeconomic status (SES). SES indicators are strongly correlated with maternal height and with BMI during the first and second trimesters of pregnancy independently of HIV status.

SPONSORSHIP

The National Institute of Child Health and Human Development (NICHD R01 32257), and the Fogarty International Center (NIH D43 TW00004).