Birthweight differences between USA and China and their relevance to breast cancer aetiology

Fetal growth velocity references from a Chinese population-based fetal growth study

BACKGROUND

Fetal growth velocity standards have yet to be established for the Chinese population. This study aimed to establish such standards suitable for the Chinese population.

METHODS

We performed a multicenter, population-based longitudinal cohort study including 9075 low-risk singleton pregnant women. Data were collected from the clinical records of 24 hospitals in 18 provinces of China. Demographic characteristics, reproductive history, fetal ultrasound measurements, and perinatal outcome data were collected. The fetal ultrasound measurements included biparietal diameter (BPD), abdominal circumference (AC), head circumference (HC), and femur diaphysis length (FDL). We used linear mixed models with cubic splines to model the trajectory of four ultrasound parameters and estimate fetal weight. Fetal growth velocity was determined by calculating the first derivative of fetal size curves. We also used logistic regression to estimate the association between fetal growth velocities in the bottom 10th percentile and adverse perinatal outcomes.

RESULTS

Fetal growth velocity was not consistent over time or among individuals. The estimated fetal weight (EFW) steadily increased beginning at 12 gestational weeks and peaked at 35 gestational weeks. The maximum velocity was 211.71 g/week, and there was a steady decrease in velocity from 35 to 40 gestational weeks. The four ultrasound measurements increased in the early second trimester; BPD and HC peaked at 13 gestational weeks, AC at 14 gestational weeks, and FDL at 15 gestational weeks. BPD and HC also increased from 19 to 24 and 19 to 21 gestational weeks, respectively. EFW velocity in the bottom 10th percentile indicated higher risks of neonatal complications (odds ratio [OR] = 2.23, 95% confidence interval [CI]: 1.79-2.78) and preterm birth < 37 weeks (OR = 3.68, 95% CI: 2.64-5.14). Sensitivity analyses showed that EFW velocity in the bottom 10th percentile was significantly associated with more adverse pregnancy outcomes for appropriate-for-gestational age neonates.

CONCLUSIONS

We established fetal growth velocity curves for the Chinese population based on real-world clinical data. Our findings demonstrated that Chinese fetal growth patterns are somewhat different from those of other populations. Fetal growth velocity could provide more information to understand the risk of adverse perinatal outcomes, especially for appropriate-for-gestational age neonates.

Excessive gestational weight gain in the first and second trimester is a risk factor for gestational diabetes mellitus among women pregnant with singletons: A repeated measures analysis

AIMS/INTRODUCTION

To evaluate gestational weight gain (GWG) in the first and second trimester as a risk factor for gestational diabetes mellitus (GDM) among women pregnant with singletons.

MATERIALS AND METHODS

This was a cohort study of women with singleton pregnancies who delivered between 1 January 2013 and 31 October 2014 in a Chinese hospital. We collected data from medical records from the first antenatal visit to delivery. All pregnant women were subjected to an oral glucose tolerance test for diagnosis of GDM during the second trimester. GWG in the first and second trimester was calculated by subtracting the prepregnancy weight from weight within 4 weeks of the oral glucose tolerance test. We categorized GWG into insufficient, appropriate and excessive according to the Institute of Medicine guidelines and population quantiles. Univariable and multivariable analyses were used to determine the association between GWG and GDM risk.

RESULTS

Of 10,422 pregnant women, we identified 8,356 eligible women with 1,622 (19.4%) diagnosed with GDM. Univariable analysis showed that GWG that exceeded the Institute of Medicine recommendation might be associated with risk of GDM (P < 0.05), but this association was not observed by multivariable analysis (adjusted odds ratio 1.07, [95% confidence interval 0.94-1.21]). Univariable and multivariable analyses both showed that GWG exceeding the 90th and 95th quantiles of included women, respectively, were at increased risk for GDM (adjusted odds ratio >P90 vs P10 -P90 adjusted odds ratio 1.31, [95% confidence interval 1.12-1.52]; >P95 vs P5 -P95 adjusted odds ratio 1.45 [95% confidence interval 1.16-1.81]).

CONCLUSIONS

Excessive GWG in the first and second trimester might be a risk factor for GDM, which highlights the importance of appropriate weight gain during pregnancy.

Genetic and environmental factors affecting birth size variation: a pooled individual-based analysis of secular trends and global geographical differences using 26 twin cohorts

Background

The genetic architecture of birth size may differ geographically and over time. We examined differences in the genetic and environmental contributions to birthweight, length and ponderal index (PI) across geographical-cultural regions (Europe, North America and Australia, and East Asia) and across birth cohorts, and how gestational age modifies these effects.

Methods

Data from 26 twin cohorts in 16 countries including 57 613 monozygotic and dizygotic twin pairs were pooled. Genetic and environmental variations of birth size were estimated using genetic structural equation modelling.

Results

The variance of birthweight and length was predominantly explained by shared environmental factors, whereas the variance of PI was explained both by shared and unique environmental factors. Genetic variance contributing to birth size was small. Adjusting for gestational age decreased the proportions of shared environmental variance and increased the propositions of unique environmental variance. Genetic variance was similar in the geographical-cultural regions, but shared environmental variance was smaller in East Asia than in Europe and North America and Australia. The total variance and shared environmental variance of birth length and PI were greater from the birth cohort 1990-99 onwards compared with the birth cohorts from 1970-79 to 1980-89.

Conclusions

The contribution of genetic factors to birth size is smaller than that of shared environmental factors, which is partly explained by gestational age. Shared environmental variances of birth length and PI were greater in the latest birth cohorts and differed also across geographical-cultural regions. Shared environmental factors are important when explaining differences in the variation of birth size globally and over time.

The pattern of gestational weight gains among Chinese women: a repeated measure analysis

This study aimed to investigate the pattern of gestational weight gain (GWG) among Chinese women. We included pregnant women, who delivered at a referral medical center in China and had no pre-specified adverse pregnancy outcomes. We collected weight data across all pregnancy visits, and used the two-level spline linear model to fit for the pattern of GWG according to pre-pregnancy BMI categories. In total, 4,567 pregnant women with 47,699 repeated measures were eligible. For those who were underweight, normal and overweight before pregnancy, the interquartile ranges (25^th to 75^th quartiles) of GWG between 14 and 36 gestational weeks were 12.9–17.7 kg, 12.6–17.3 kg and 11.7–16.8 kg, and the corresponding rates of GWG were 2.62 kg/month, 2.56 kg/month and 2.37 kg/month. For underweight and normal women, the rates of GWG were similar before 14 weeks (0.57 and 0.58 kg/month) and after 36 weeks (1.69 and 1.70 kg/month); however, the rates of GWG were higher for overweight women (0.66 kg/month before 14 weeks and 1.89 kg/month after 36 weeks). In summary, the pattern of GWG among Chinese pregnant women is generally consistent with the IOM recommendation, particularly for those who are normal or underweight. Modifications are, however, warranted for overweight pregnant women.

Size at birth and risk of breast cancer: update from a prospective population-based study

Birth size variables (birth weight, birth length and head circumference) have been reported to be positively associated with adult breast cancer risk, whereas a possible association of placental weight has not been adequately studied. It has also been suggested that maternal height may modify the association of birth size with adult breast cancer risk, but this has not been studied in detail. We updated a long-term follow-up of 22,931 Norwegian women (average of 51 years of follow up during which 870 women were diagnosed with breast cancer) and assessed placental weight in relation to breast cancer risk, in addition to providing updated analyses on breast cancer risk in relation to birth weight, birth length and head circumference. Placental weight was not associated with risk for breast cancer in adulthood, but there was a positive association of breast cancer risk with birth length (HR 1.13, 95% CI 1.05-1.21, per 2 cm increment), though not with birth weight (HR 1.02, 95% CI 0.95-1.10 per 0.5 kg increment). For birth length, the graded increase in risk was particularly strong among women whose mothers were relatively tall (p for trend, 0.001), compared to the trend among women whose mothers were relatively short (p for trend, 0.221). The results showed a robust and positive association of birth length with breast cancer risk, and may be especially strong in women whose mothers were relatively tall. We found no association of placental weight with risk for breast cancer.

High Bab Birth Weight Andof Hormone-Associated Cancer in Mothers: The Cancer–Cardiovascular Disease Dichotomy and its Possible Causes

The idea of intrauterine or fetal factors being the cause of several prevalent noninfectious diseases in adults has recently gained the status of an axiom. One of the most thoroughly studied predictors is birth weight (BW). Although many published studies point at relations between BW and later adult morbidity or mortality, much less attention is paid to associations between baby BW and maternal morbidity. Available data suggest a sort of dichotomy in these relationships. Thus, cardiovascular risk is higher in mothers of babies with a reduced BW, while cancer risk, mainly of the breast and some other hormone-dependent cancers, is often higher among mothers of babies with a large BW (newborn macrosomia). This review addresses possible causes and endocrine mechanisms of this topic and suggests a ‘particular’ and ‘general’ solution for arising controversy. Emphasis is placed on a probable competition between chronic diseases (mainly, between female hormone-related cancer and cardiovascular pathology) within the concept of multiple causes of death. These associations should be remembered while studying the relation between offspring BW and maternal predisposition to hormone-associated cancers and other noncommunicable diseases.

Weight loss before conception: A systematic literature review

The prevalence of overweight and obesity in women has increased during the last decades. This is a serious concern since a high BMI before conception is an independent risk factor for many adverse outcomes of pregnancy. Therefore, dietary counseling, intended to stimulate weight loss in overweight and obese women prior to conception has recently been recommended. However, dieting with the purpose to lose weight may involve health risks for mother and offspring. We conducted a systematic literature review to identify papers investigating the effects of weight loss due to dietary interventions before conception. The objective of this study is to assess the effect of weight loss prior to conception in overweight or obese women on a number of health-related outcomes in mother and offspring using studies published between January 2000 and December 2011. Our first literature search produced 486 citations and, based on predefined eligibility criteria, 58 were selected and ordered in full text. Two group members read each paper. Fifteen studies were selected for quality assessment and two of them were considered appropriate for inclusion in evidence tables. A complementary search identified 168 citations with four papers being ordered in full text. The two selected studies provided data for overweight and obese women. One showed a positive effect of weight loss before pregnancy on the risk of gestational diabetes and one demonstrated a reduced risk for large-for-gestational-age infants in women with a BMI above 25 who lost weight before pregnancy. No study investigated the effect of weight loss due to a dietary intervention before conception. There is a lack of studies on overweight and obese women investigating the effect of dietary-induced weight loss prior to conception on health-related variables in mother and offspring. Such studies are probably lacking since they are difficult to conduct. Therefore, alternative strategies to control the body weight of girls and women of reproductive age are needed.

Birth weight and other prenatal factors and risk of breast cancer in Asian-Americans

Little is known about the role of birth weight and other prenatal factors in the etiology of breast cancer in Asian-Americans. We investigated the relation between birth weight and other prenatal factors and breast cancer risk in a population-based case-control study in Los Angeles County that included 2,259 Asian-American women with incident, histologically confirmed breast cancer and 2,019 control women, who were frequency matched to cases on age, Asian ethnicity, and neighborhood of residence. Breast cancer risk nearly doubled (odds ratio (OR) = 1.97, 95% confidence interval (CI) = 1.15-3.39) among those with high (≥ 4000 g) birth weight compared to those with low (<2500 g) birth weight after adjusting for age at menarche, parity, adult body mass index, and other covariates. Risk increased 8% per 500 g increase in birth weight (P trend = 0.10). We observed a significant relationship between birth weight and age at menarche in both cases and controls. Mean birth weight was higher (2948 g) for control women who had early menarche (age ≤ 11 years) compared to those who had menarche late (age ≥ 15 years) (2807 g) (P trend = 0.016); results were similar among case patients (P trend = 0.020). Older maternal age was also a risk factor; risk increased by 6% (95% CI = 1.01-1.12) per 5 years increase in maternal age with adjustment for parity and other risk factors. Our results support the hypothesis that high birth weight and older maternal age at pregnancy may have contributed to the rising breast cancer incidence in Asian-Americans.

Mothers' pre-pregnancy BMI and weight gain during pregnancy and risk of breast cancer in daughters

Previous studies have established that higher birthweight is associated with increased risk of breast cancer. However, the mechanisms underlying this association remain unclear. We explored whether maternal pregnancy weight gain and pre-pregnancy body mass index (BMI), which influence birthweight, are associated with risk of breast cancer in offspring. The Nurses' Mothers case-control study of breast cancer was nested in the Nurses' Health Study I and II cohorts. Mothers of 814 nurses with and 1,809 nurses without breast cancer completed questionnaires with information on pre-pregnancy height and weight, pregnancy weight gain, and other aspects of their pregnancies with the nurse daughters. We calculated odds ratios for breast cancer using conditional logistic regression. Mean pregnancy weight gain was 23 lb, and average pre-pregnancy BMI was 21 kg/m². Mothers' weight gain during pregnancy was not associated with the daughters' risk of breast cancer. Compared to women whose mothers gained 20-29 lb, women whose mothers gained less than 10 lb had a relative risk of 0.92 (95% confidence interval [CI]: 0.62-1.36), adjusting for the age of the nurses. Women whose mothers gained 40 or more pounds had a relative risk of 0.82 (95% CI: 0.55-1.23). Mothers' pre-pregnancy BMI was not associated with the daughters' risk of breast cancer. Women whose mothers had a pre-pregnancy BMI of 30 or more had a relative risk of 0.77 (95% CI: 0.34-1.74) compared to those with BMI less than 20. Additional adjustment for prenatal factors or for nurses' characteristics later in life had no effect on the results. The association between birthweight and breast cancer risk is likely due to factors independent of mothers' weight gain during pregnancy or pre-pregnancy BMI. Because BMIs and pregnancy weight gains were lower in this population than today, we cannot rule out associations for very high pre-pregnancy BMIs or pregnancy weight gains.

Non-linear and gender-specific relationships among placental growth measures and the fetoplacental weight ratio

GOALS

Fetal growth depends on placental growth; the fetoplacental weight ratio (FPR) is a common proxy for the balance between fetal and placental growth. Male and female infants are known to have differing vulnerabilities in fetal life, during parturition and in infancy. We hypothesized that these differences may be paralleled by differences in how birth weight (BW) and the fetoplacental weight ratio (FPR) are affected by changes in placental proportions.

MATERIALS AND METHODS

Placental proportion measures (disk shape, larger and smaller chorionic diameters, chorionic plate area calculated as the area of an ellipse with the 2 given diameters, disk thickness, cord eccentricity and cord length) were available for 24,601 participants in the Collaborative Perinatal Project delivered between >34 and <43 completed weeks. The variables were standardized and entered into multiple automated regression splines (MARS 2.0, Salford Systems, Vista CA) to identify nonlinearities in the relationships of placental growth measures to BW and FPR with results compared for male and female infants.

RESULTS

Changes in chorionic plate growth in female compared to male infants resulted in a greater change in BW and FPR. The positive effects of umbilical cord length on BW reversed at the mean umbilical cord length in females and at +0.08 SD in male infants.

CONCLUSIONS

Female infants' BW and FPR are each more responsive to changes in placental chorionic plate growth dimensions than males; this may account for greater female resilience (and greater male vulnerability) to gestational stressors. The effect of umbilical cord length on FPR may be due to longer cords carrying greater fetal vascular resistance. Again male fetuses show a higher "threshold" to the negative effects of longer cords on FPR.

Insulin-like growth factor levels in cord blood, birth weight and breast cancer risk

Breast cancer incidence and birth weight are higher among Caucasian than Asian women, and birth size has been positively associated with breast cancer risk. Pregnancy hormone levels, however, have been generally lower in Caucasian than Asian women. We studied components of the insulin-like growth factor (IGF) system in cord blood from 92 singleton babies born in Boston, USA, and 110 born in Shanghai, China, in 1994–1995. Cord blood IGF-1 was significantly higher among Caucasian compared with Chinese babies (P<10⁻⁶). The opposite was noted for IGF-2 (P∼10⁻⁴). IGF-1 was significantly positively associated with birth weight and birth length in Boston, but not Shanghai. In contrast, stronger positive, though statistically non-significant, associations of IGF-2 with birth size were only evident in Shanghai. The associations of birth weight and birth length were positive and significant in taller women (for IGF-1 in Boston P∼0.003 and 0.03, respectively; for IGF-2 in Shanghai P∼0.05 and ∼0.04, respectively), among whom maternal anthropometry does not exercise strong constraints in foetal growth. The documentation of higher cord blood levels of IGF-1, a principal growth hormone that does not cross the placenta, among Caucasian than in Asian newborns is concordant with breast cancer incidence in these populations.

Early life events and conditions and breast cancer risk: from epidemiology to etiology

Risk factors for breast cancer--documented by intensive epidemiological investigations and viewed in the context of general principles of carcinogenesis--can be integrated to an etiologic model comprising 3 principal components: the likelihood of breast cancer occurrence depends on the number of mammary tissue-specific stem cells, which is determined in early life; all growth-enhancing mammotropic hormones affect the rate of expansion of initiated clones; and while a pregnancy stimulates the replication of already initiated cells, it conveys long-term protection through differentiation of mammary tissue-specific stem cells. This perspective accommodates much of what is known about the epidemiology and natural history of breast cancer and highlights the role of early life in the origin of this cancer.

Plasma volume expansion in pregnancy: implications for biomarkers in population studies

There is a growing body of literature focused on endogenous hormone exposures during pregnancy and subsequent cancer risk for both mother and offspring. Examples of these studies include those focused on the biological mechanism for the association of preeclampsia with reduced risk of breast cancer for mother and female offspring or studies that have examined hormone concentrations during pregnancy between different ethnic groups who vary in their rates of breast cancer incidence. Although these studies seem relatively straightforward in conception and analysis, measurement of the concentration of hormones and other biomarkers in pregnant subjects is influenced by plasma volume expansion (PVE). During pregnancy, the maternal plasma volume expands 45% on average to provide for the greater circulatory needs of the maternal organs. Consequently, serum protein and hormone concentrations are greatly altered when comparing the pregnant with nonpregnant state. Assessing PVE also is complicated by the vast individual variation in PVE, ranging from minimal to a 2-fold increase. We propose that PVE needs to be evaluated when comparing biomarker concentrations during pregnancy in two populations that may differ with respect to PVE. Small body size is associated with lower PVE compared with higher body size. Therefore, we hypothesize that variation in PVE will influence the interpretation of differences in biomarker concentrations across population groups with respect to the etiologic significance of the biomarker to the disease under study (e.g., breast cancer). It is possible that some observations may be due only to differences in dilution between the two groups. We present PVE as a topic for consideration in population-based studies, examples of the types of studies where PVE may be relevant, and our own analysis of one such study in the text below.

Levels and correlates of alpha-fetoprotein in normal pregnancies among Caucasian and Chinese women

Alpha-fetoprotein has been suggested to have anti breast cancer properties both in adult life and in utero. We studied correlates of maternal serum alpha-fetoprotein levels in normal singleton pregnancies. This was a prospective study relying on women attending maternal units in major teaching hospitals in Boston, USA and Shanghai, China. Specifically, 212 Caucasian women in Boston, and 196 Asian women in Shanghai provided blood samples at the 16th and 27th gestational week. Maternal serum alpha-fetoprotein levels were measured and correlated with maternal and newborn parameters through multiple regression procedures, controlling for a set of potential confounders, including maternal levels of measured hormones. Alpha-fetoprotein was strongly inversely associated with maternal prepregnancy body mass index (-4.73 ng/l at the 27th week per 1 kg/m of body mass index, with 95% confidence intervals -7.09 to -2.36), whereas it was not related to parity, gender of offspring or birth weight. Duration of gestation was inversely associated with maternal alpha-fetoprotein levels, particularly among Caucasian women (-0.22 weeks per 60 ng/l of alpha-fetoprotein at the 27th week, with 95% confidence intervals -0.39 to -0.05). In normal pregnancies, maternal alpha-fetoprotein is inversely related to prepregnancy body mass index and appears to have a physiologic role on duration of gestation rather than on birth weight.

Parental characteristics as predictors of birthweight

BACKGROUND

Previous studies provided conflicting results on the relevance of parental characteristics for offspring's size at birth. The objective of this study was to investigate parental predictors of birthweight.

METHODS

In this cross-sectional study, 34,063 women in the Nurses' Mother's Cohort were queried about parental characteristics during the pregnancy with and birthweight of their nurse daughter.

RESULTS

The predictive linear regression model of birthweight included 13 factors and the majority of the predictive power came from parental anthropometric factors. In the adjusted analysis, daily consumption of each additional glass of milk was associated with an increase of approximately 6 g in birthweight (P for trend = 0.01) and daily consumption of each additional cup of coffee was associated with a decrease of approximately 10 g in birthweight (P for trend < 0.0001). Drinking 1-2, 3-4 and 5+ cups of coffee daily was associated with a 28% [95% confidence interval (CI) 0.12, 0.47], 30% (95% CI 0.10, 0.55) and 63% (95% CI 0.25, 1.12) increase, respectively, in the odds of intrauterine growth restriction when compared with non-drinkers.

CONCLUSIONS

The present study confirmed several previously reported determinants of birthweight. Maternal dietary intake of milk and coffee during pregnancy may influence fetal growth.

Early Life Diet and the Risk for Adult Breast Cancer

A hypothesis postulating intrauterine and early life influences on the occurrence of breast cancer in adult life has received considerable support in the literature. We present alternative or complementary ways through which diet could affect breast cancer risk in this context. Emphasis is placed on evidence that reduced energy intake in early life is associated with smaller body size, which, in turn, constrains birth weight and subsequent development of offspring and is associated with reduced breast cancer risk.

Role of birthweight in the etiology of breast cancer

Breast cancer may originate in utero. We reviewed the available evidence on the association between birthweight and the risk of breast cancer. To date, 26 research papers addressing this issue have been published. The majority of studies identified a positive link between birthweight and premenopausal, but not postmenopausal, breast cancer. The relative risk estimate for breast cancer comparing women with high birthweight to women with low birthweight combining all studies including both pre- and postmenopausal breast cancer was 1.23 (95% confidence interval 1.13-1.34). The mechanisms underlying this association likely include elevated levels of growth factors that may increase the number of susceptible stem cells in the mammary gland or initiate tumors through DNA mutations. Loss of imprinting (LOI) of growth hormone genes relevant for intrauterine growth, such as insulin-like growth factor 2 (IGF2), leads to abnormally high levels of these hormones evidenced by high birthweight. LOI of IGF2 has also been found in mammary tumor tissue. The role of environmental factors that stimulate such epigenetic regulation of gene expression remains to be elucidated.

The bigger the healthier: are the limits of BMI risk changing over time?

The body mass index (BMI) is often used as a predictor of overweight and obesity. There is, however, an important debate among international specialists as to what the risk limits should be, and where the cut-off points should be located. In the United States, for instance, adults with a BMI between 25 and 30 are considered overweight, while adults with a BMI of 30 or higher are considered obese. Nevertheless some researchers, especially in developing countries, claim that the limits established for the US are too permissive, and that the threshold to define obese adults should be set lower for other nationalities and ethnicities. This paper analyzes the mortality risks for different BMI levels of two populations of American adult men. The first population lived during the last quarter of the 19th century and the early 20th century. These men were drawn from a random sample of Union Army veterans who fought during the American Civil War (1861-1865). A contemporary sample of men was drawn from the first wave of the National Health and Nutrition Examination Survey (NHANES I) conducted between 1971 and 1975. The results indicate that the frontier of overweight and obesity are expanding over time, such that the potential risk is nowadays associated with higher levels of BMI. The finding may imply that differences in BMI cut-off points are not only cross ethnic, but also occur for similar ethnicities across time.

Maternal height, pregnancy estriol and birth weight in reference to breast cancer risk in Boston and Shanghai

Birth weight has been positively associated with breast cancer risk in adult life and is positively associated with the principal pregnancy estrogen estriol. Birth weight is lower among Chinese women than among Caucasian women, but paradoxically, pregnancy estriol levels are higher among the former than the latter. We studied a cohort of 317 Caucasian pregnant women in Boston, MA, and 339 Chinese pregnant women in Shanghai, China. We investigated whether maternal height, which is inversely associated with pregnancy estriol levels, interacts with this hormone in relation to birth weight, thus accommodating the apparently contradictory ecologic and analytic evidence concerning the role of pregnancy estrogens on breast cancer risk in the offspring. In both Boston and Shanghai, there was a positive association of pregnancy estriol with birth weight among taller women, whereas among shorter women the association was essentially null. The relevant interaction terms were highly significant in Boston (p approximately 0.006), whereas in Shanghai, where pregnant women were generally shorter, the interaction term was suggestive (p approximately 0.14). We conclude that maternal height should be considered an important risk factor for breast cancer in the offspring since it is a crucial determinant of birth weight, both directly and through positive interaction with the principal pregnancy estrogen estriol.

Towards an integrated model for breast cancer etiology: the crucial role of the number of mammary tissue-specific stem cells

Perinatal events and conditions, notably birth weight, are associated with breast cancer risk in offspring, and correlates of mammary gland mass are predictors of breast cancer risk. These findings may be interpreted as indicating that high levels of estrogens and components of the insulin-like growth factor system during pregnancy favour the generation of mammary tissue-specific stem cells, and that the number of these cells, which is positively associated with mammary gland mass, is an important determinant of breast cancer risk. Perinatal events and conditions may also affect risk for other malignancies, but the evidence in the case of breast cancer is prominent, possibly because estrogens and the insulin-like growth factor system are both involved in breast cancer etiology and affect birth weight.

Diet during pregnancy in relation to maternal weight gain and birth size

OBJECTIVE

Maternal weight gain has been consistently linked to birth weight but, beyond maternal energy intake, no macronutrient has been associated with either of them. We have examined whether maternal energy-adjusted intake of macronutrients is associated with either maternal weight gain or birth-size parameters.

DESIGN

Cohort study.

SETTING

University hospital in Boston, USA.

SUBJECTS

A total of 224 pregnant women coming for their first routine prenatal visit. The women were followed through delivery.

INTERVENTIONS

None. Pregnant women's dietary intake during the second trimester was ascertained at the 27th week of pregnancy through a food frequency questionnaire.

RESULTS

Intake of neither energy nor any of the energy-generating nutrients was significantly associated with birth size. In contrast, maternal weight gain by the end of the second trimester of pregnancy was significantly associated with energy intake (+0.9 kg/s.d. of intake; P approximately 0.006) as well as energy-adjusted intake of protein (+3.1 kg/s.d. of intake; P<10(-4)), lipids of animal origin (+2.6 kg/s.d. of intake; P<10(-4)) and carbohydrates (-5.2 kg/s.d. of intake; P<10(-4)).

CONCLUSIONS

Although maternal weight gain is strongly associated with birth size, the indicated nutritional associations with weight gain are not reflected in similar associations with birth-size parameters. The pattern is reminiscent of the sequence linking diet to coronary heart disease (CHD) through cholesterol: diet has been conclusively linked to blood cholesterol levels and cholesterol levels are conclusively linked to this disease, even though the association of diet with CHD has been inconclusive and controversial.