Low vitamin D in the first trimester linked to a higher risk of preterm birth and reduced fetal length

Low vitamin D in the first trimester linked to a higher risk of preterm birth and reduced fetal length

Findings suggest that early pregnancy may be a critical window for maternal vitamin D to support fetal growth and reduce risk of preterm birth

A current oneAmerican Journal of Clinical NutritionThe study examined whether first and second trimester vitamin D levels with maternal vitamin D are associated with fetal growth and pregnancy outcomes.

Vitamin D status and pregnancy outcome

In an American survey, approximately 28% of pregnant or lactating women were vitamin D deficient. Several studies have shown that inadequate maternal vitamin D status, that is, below 50 nmol/L, can lead to adverse pregnancy outcomes for both infant and mother. Vitamin D deficiency has been associated with an increased risk of gestational diabetes mellitus, preterm birth and preeclampsia.

Vitamin D plays an important role in early pregnancy. For example, it is involved in the production of vascular endothelial growth factor and placental growth factor. These pro-angiogenic factors are critical for regulating early placental vascularization. In addition, vitamin D is extremely important for bone health and formation. Previous studies have linked maternal vitamin D status to birth weight and skeletal development.

Not many studies have examined whether vitamin D status influences fetal growth patterns across pregnancy. Previous research has presented conflicting evidence regarding the effectiveness of vitamin D supplements in improving maternal and newborn outcomes. Therefore, it is important to evaluate the effects of vitamin D supplementation at different times during pregnancy on maternal outcomes and fetal growth patterns.

About the study

The current longitudinal study examined the associations between first and second trimester vitamin D status and fetal growth pattern, including gestational age at birth, small for gestational age (SGA), and risk of preterm birth.

All relevant data were obtained from a multicenter prospective cohort study - the Study of Nulliparous Pregnancy Outcomes: Surveillance of Prospective Mothers (NUMOM2B). This US-based study included 10,038 nulliparous pregnant women. Pregnancy data and biospecimens were collected from participants in their first trimester, early second trimester, late second/early third trimester, and at delivery.

Since 25-hydroxyvitamin D (25(OH)d) was not originally measured for the Numom2b cohort. A total of 351 Numom2b participants were randomly selected to measure F25(OH)D for the current study. Fetal growth was measured by post-pregnancy ultrasound at 16–21 and 22–29 weeks. In addition, neonatal anthropometric estimates were measured at birth. Fetal growth curves were constructed based on length, weight, and head circumferencee.g-Cores.

Study results

The average age of the participants was 27.9 years, the average length of pregnancy was 38.8 weeks, and the average body mass index (BMI) was 26.6. Approximately 50% of the cohort had a bachelor's degree, and most were non-Hispanic white. Compared to older participants, younger women were more likely to have a vitamin D deficiency.

Interestingly, participants with a bachelor's degree were less likely to be vitamin D deficient, i.e. 25(OH)d <50 nmol/L. These participants showed a higher propensity to use multivitamin supplements. The mean 25(OH)D concentrations in the first and second trimesters were 68.1 nmol/L and 78.0 nmol/L, respectively.

In the first trimester, 20% of women had 25(OH)D concentrations below 50 nmol/L, while the majority showed 25(OH)D concentrations above 50 nmol/L. In the second trimester, 13% of women demonstrated vitamin D deficiency, while 87% had 25(OH)D concentrations ≥50 nmol/L.

96% of the cohort had fetal growth measures for all threefold points, while the remaining 4% had measures for only twofold points. Associations between 25(OH)D and linear fetal growth were observed in the first trimester. However, vitamin D concentration was not associated with either weight or head circumference in adjusted models.

In the first trimester, 10 nmol/L was associated with 25 (OH) D with a length of around 0.05.e.g-After adjusting for disruptive factors. Using Institute of Medicine (IOM) insufficiency disorders (<50 versus ≥50 nmol/L), second trimester 25(OH)D was not associated with fetal growth trajectories for length, weight, or head circumference after adjusting for confounding factors.

Approximately 6% of infants were born SGA and 8% were born preterm. In the current study, the first trimester was assessed 25 (OH) d continuously or using IOM binary intercepts. 25(OH)D concentration was not associated with risk of SGA or preterm birth.

Compared to women with 25 (OH) d > 80 nmol/L was found earlier. Second trimester 25(OH)D was not associated with SGA or preterm birth.

Conclusions

In the current study, maternal first trimester vitamin D status was found to be robustly associated with fetal growth patterns. Vitamin D deficiency in the first trimester was associated with a higher risk of shorter mean pregnancy and preterm birth. However, in the second trimester, vitamin D status was not associated with adverse pregnancy outcomes or changes in fetal growth patterns. In the future, researchers need to uncover the mechanism by which vitamin D contributes to fetal growth.

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