The association between folic acid supplementation and birth defects other than neural tube defects (NTD) remains unclear. We used a log-binomial regression model to investigate if periconceptional folic acid and/or multivitamin use was associated with birth defects in Norway with prospectively collected data from the Medical Birth Registry of Norway (MBRN) during 1999–2013. We used the European Surveillance of Congenital Anomalies (EUROCAT) classification system to define eleven organ-specific major birth defect groups (nervous system, eye, ear–face–neck, cardiovascular system, respiratory system, oral clefts, digestive system, abdominal wall, urinary system, genital organs and limb), with additional subgroups. Fetuses or infants whose mothers used folic acid and/or multivitamin supplements before and during pregnancy were classified as exposed. During the years 1999–2013, 888 294 (99·0 %) live-born infants, 6633 (0·7 %) stillborn infants and 2135 (0·2 %) fetuses from terminated pregnancies due to fetal anomalies were registered in the MBRN. Among the live- and stillborn infants of women who used vitamin supplements compared with infants of non-users, the adjusted relative risk (aRR) was 0·94 (95 % CI 0·91, 0·98) for total birth defects (n 18 382). Supplement use was associated with reduced risk of abdominal wall defects (aRR 0·58; 95 % CI 0·42, 0·80, n 377), genital organ defects (aRR 0·81; 95 % CI 0·72, 0·91, n 2299) and limb defects (aRR 0·81; 95 % CI 0·74, 0·90, n 3409). Protective associations were also suggested for NTD, respiratory system defects and digestive system defects although CI included the null value of 1. During the full study period, statistically significant associations between supplement use and defects in the eye, ear–face–neck, heart or oral clefts were not observed.

The first positive genome-wide association study on gestational length and preterm delivery showed the involvement of an Se metabolism gene. In the present study, we examine the association between maternal intake of Se and Se status with gestational length and preterm delivery in 72 025 women with singleton live births from the population-based, prospective Norwegian Mother, Father and Child Cohort Study (MoBa). A self-reported, semi-quantitative FFQ answered in pregnancy week 22 was used to estimate Se intake during the first half of pregnancy. Associations were analysed with adjusted linear and Cox regressions. Se status was assessed in whole blood collected in gestational week 17 (n 2637). Median dietary Se intake was 53 (interquartile range (IQR) 44–62) µg/d, supplements provided additionally 50 (IQR 30–75) µg/d for supplement users (n 23 409). Maternal dietary Se intake was significantly associated with prolonged gestational length (β per sd = 0·25, 95 % CI, 0·07, 0·43) and decreased risk of preterm delivery (n 3618, hazard ratio per sd = 0·92, 95 % CI, 0·87, 0·98). Neither Se intake from supplements nor maternal blood Se status was associated with gestational length or preterm delivery. Hence, the present study showed that maternal dietary Se intake but not intake of Se-containing supplements, during the first half of pregnancy was significantly associated with decreased risk of preterm delivery. Further investigations, preferably in the form of a large randomised controlled trial, are needed to elucidate the impact of Se on pregnancy duration.

The rising prevalence of overweight and obesity is a worldwide public health challenge. Pregnancy and beyond is a potentially important window for future weight gain in women. We investigated associations between maternal adherence to the New Nordic diet (NND) during pregnancy and maternal BMI trajectories from delivery to 8 years post delivery. Data are from the Norwegian Mother and Child Cohort. Pregnant women from all of Norway were recruited between 1999 and 2008, and 55 056 are included in the present analysis. A previously constructed diet score, NND, was used to assess adherence to the diet. The score favours intake of Nordic fruits, root vegetables, cabbages, potatoes, oatmeal porridge, whole grains, wild fish, game, berries, milk and water. Linear spline multi-level models were used to estimate the association. We found that women with higher adherence to the NND pattern during pregnancy had on average lower post-partum BMI trajectories and slightly less weight gain up to 8 years post delivery compared with the lower NND adherers. These associations remained after adjustment for physical activity, education, maternal age, smoking and parity (mean diff at delivery (high v. low adherers): −0·3 kg/m2; 95 % CI −0·4, −0·2; mean diff at 8 years: −0·5 kg/m2; 95 % CI −0·6, −0·4), and were not explained by differences in energy intake or by exclusive breast-feeding duration. Similar patterns of associations were seen with trajectories of overweight/obesity as the outcome. In conclusion, our findings suggest that the NND may have beneficial properties to long-term weight regulation among women post-partum.

Results from previous studies on maternal folic acid intake and infant oral clefts are inconclusive. The aim of the present study was to investigate the association between women’s use of folic acid and/or multivitamin supplements and the risk for oral cleft in the newborn. We used data from the Medical Birth Registry of Norway based on all births in Norway from 1999 to 2013. A total of 528 220 women had 880 568 pregnancies, resulting in 896 674 live births and stillbirths, of which 1623 had oral clefts (isolated oral clefts, n 1311; non-isolated oral clefts, n 312). Altogether, 21·5 % of women were vitamin supplement users before pregnancy. The birth prevalence of oral clefts was 1·81/1000 live births and stillbirths. Relative risks (RR) were estimated with log-binomial regression. For pregnancies with maternal use of vitamins, the adjusted RR for clefts overall was 0·90 (95 % CI 0·79, 1·04). The adjusted RR for cleft palate only (n 586) was 0·84 (95 % CI 0·66, 1·06) and that for cleft lip with or without cleft palate (n 1037) was 0·94 (95 % CI 0·79, 1·13). Associations were stronger for cleft cases that occurred in combination with other malformations (adjusted RR 0·63; 95 % CI 0·45, 0·88), although vitamin supplements provided no protection against isolated clefts (adjusted RR 0·98; 95 % CI 0·84, 1·15). In conclusion, our study demonstrates no statistically significant association between vitamin use and isolated oral clefts. However, we found lower risk for oral clefts that occurred in combination with other malformations.