Table 2.

Description of intervention studies of vitamin D supplementation and observational studies of vitamin D intake (including supplements) eligible for inclusion in meta-analyses

Study ID	Country and latitudea	Population	Intervention or exposure	Comments and GRADE assessment of risk of bias
Intervention studies
Brooke (1980)63, 70, 91	UK (London) 51°N	Affluent Asian immigrants in 3rd trimester. Excluded preterm deliveries, congenital malformations, and certain maternal illnesses. Mean 25(OH)D: 20.1 nmol/L at 28 weeks.	Randomized to a daily dose of 1) 1000 IU Vitamin D2 (n=59) or 2) Placebo (n=67) provided from 28–32 weeks gestation to delivery.	Double blind RCT. Small sample size GRADE: Moderate
Hollis (2011)5,b	US (South Carolina) 34°N	Multiethnic population, mean age 27 years, women with pregnancy <16 weeks gestation at enrollment. All participants received prenatal multivitamin/mineral supplement. Mean baseline 25(OH)D by group: 58.2–61.6 nmol/L.	Randomized to daily dose of 1) 400 IU vitamin D3 (n=111) 2) 2000 IU vitamin D3 (n=122) 3) 4000 IU vitamin D3 (n=117) provided from 12–16 wks until delivery. Women with baseline 25(OH)D levels >100nmol/L randomized to group 1 or 2.	Double blind RCT. Loss to follow-up, potential selection bias due to randomization process. Grade: Moderate
Mallet (1986)88	France (Northwest) 49°N	Caucasian population, mean age 25 y, analysis included at-term infants born at term during Feb. and Mar. Mean maternal 25(OH)D in the unsupplemented group was 9.4 nmol/L.	Random assignment to (1) 1000 IU vitamin D2 daily for last 3 months of pregnancy (n=21) (2) One-time dose of 200,000 IU in 7th month of gest. (n=27) (3) No supplement (n=29).	Randomized non-placebo controlled trial; unclear whether women were randomized into the control group. GRADE: Moderate
Mayra (1988)47	India (Rohtak) 28°N	Singleton pregnancies aged 22–35 years attending antenatal clinic of a medical college. Complications including pre-eclampsia, haemorrhage or premature delivery excluded. 25(OH)D levels not assessed.	Random selection to (1) 2 doses of 600,000 IU vitamin D3, one each in month 7 and 8 of pregnancy (n=100) (2) No supplement (n=100).	Randomized non-placebo controlled trial; method of randomization unclear, no placebo, unclear dropout/number of exclusions. Grade: Low
Yu (2009)43,b	UK (London) 51°N	Multi ethnic hospital population recruited at 27 weeks gestation Excluded women with pre-existing sarcoidosis, osteomalacia, renal dysfunction, TB. Median 25(OH)D≈25nmol/L at 27 weeks.	Random selection to (1) Single oral dose of 200,000 IU Vit. D (n=60), (2): Daily supp. with 800 IU Vitamin D from 27 weeks to delivery (n=60) (3) No treatment (n=60)	Randomized non-placebo controlled trial. Small sample size, no placebo. GRADE: Moderate
Observational studies
Haugen (2009)76	Norway (nationwide) 58°–71°N	23,423 nulliparous pregnant women from the Norwegian Mother and Child Cohort study with singleton births recruited at first ultrasound exam.	FFQ uses to assess intake of vitamin D for first 4–5 months of pregnancy and supp. use assessed at week 30.	Prospective cohort study. Supplement use validated with good correlation against reported use and biomarkers. Large sample size. GRADE: Moderate
Scholl (2009)64	U.S. (Camden, NJ) 39° N	Multiethnic cohort, data from 2,215 pregnancies enrolled at entry to prenatal care. Excluded those with serious non-obstetric problems.	Dietary intake of vitamin D and supplement use assessed using 3 24 hour recalls.	Large sample size, controlled for ethnicity, BMI, energy intake, intake of key nutrients, and gestational duration for birthweight. GRADE: Moderate
Camargo (2007)60	US (Massachusetts) 42° N	1194 mother-child pairs from Project VIVA cohort. Excluded multiple gestations, non-English speakers, plans to move, and gestational age >22 weeks at initial appointment.	Dietary intake was collected using a validated semi-quantitative FFQ and intake from supplements was collected for 1st and 2nd trimesters	Large sample size, examination by quintiles of intake. Only presented unadjusted analysis for perinatal outcomes. GRADE: Low
Oken (2007)92	US (Massachusetts) 42° N	1178 women from the Project VIVA cohort recruited after median 10.4 weeks gestation. Excluded women with pre-existing hypertension.	Same as Camargo (2007) above	Large sample size, examination by quintiles of intake. GRADE: Low

^aApproximate latitude estimated by authors

^bAdditional unpublished or in-press data was also provided by author