Figure 1. The PRISMA diagram outlining the article selection process of our systematic review.
| Journal of Clinical Gynecology and Obstetrics, ISSN 1927-1271 print, 1927-128X online, Open Access |
| Article copyright, the authors; Journal compilation copyright, J Clin Gynecol Obstet and Elmer Press Inc |
| Journal website https://jcgo.elmerpub.com |
Review
Volume 15, Number 1, March 2026, pages 1-12
Seasonal Variation in Maternal Vitamin D Levels on Neonatal Outcomes: A Systematic Review
Figure
Tables
| Database | Search/MeSH term |
|---|---|
| PubMed | ("Pregnant Women"[Mesh] OR "Pregnancy"[Mesh] OR "Pregnancy Trimesters"[Mesh] OR "Pregnancy Complications"[Mesh] OR "Maternal Health Services"[Mesh] OR "pregnan*"[tiab] OR "maternal*"[tiab] OR "expectant mothers"[tiab] OR "gestational"[tiab]) AND ("Vitamin D"[Mesh] OR "Ergocalciferols"[Mesh] OR "Vitamin D Deficiency"[Mesh] OR "Vitamin D*"[tiab] OR "ergocalciferol*"[tiab]) AND ("Seasons"[Mesh] OR "Sunlight"[Mesh] OR "season*"[tiab] OR "winter"[tiab] OR "spring"[tiab] OR "autumn*"[tiab] OR "summer"[tiab] OR "time of year"[tiab] OR "sun"[tiab] OR "sunlight"[tiab] OR "sunshine"[tiab]) |
| CINAHL | ((MH "Pregnant Women+") OR (MH Pregnancy+) OR (MH "Pregnancy Trimesters+") OR (MH "Pregnancy Complications+") OR (MH "Maternal Health Services+") OR (TI pregnan* OR AB pregnan*) OR (TI maternal* OR AB maternal*) OR (TI "expectant mothers" OR AB "expectant mothers") OR (TI gestational OR AB gestational)) AND ((MH "Vitamin D+") OR (MH Ergocalciferols+) OR (MH "Vitamin D Deficiency+") OR (TI "Vitamin D*" OR AB "Vitamin D*") OR (TI ergocalciferol* OR AB ergocalciferol*)) AND ((MH Seasons+) OR (MH Sunlight+) OR (TI season* OR AB season*) OR (TI winter OR AB winter) OR (TI spring OR AB spring) OR (TI autumn* OR AB autumn*) OR (TI summer OR AB summer) OR (TI "time of year" OR AB "time of year") OR (TI sun OR AB sun) OR (TI sunlight OR AB sunlight) OR (TI sunshine OR AB sunshine)) |
| Cochrane Library | ([mh "Pregnant Women"] OR [mh Pregnancy] OR [mh "Pregnancy Trimesters"] OR [mh "Pregnancy Complications"] OR [mh "Maternal Health Services"] OR pregnan*:ti,ab OR maternal*:ti,ab OR "expectant mothers":ti,ab OR gestational:ti,ab) AND ([mh "Vitamin D"] OR [mh Ergocalciferols] OR [mh "Vitamin D Deficiency"] OR ("Vitamin" NEXT D*):ti,ab OR ergocalciferol*:ti,ab) AND ([mh Seasons] OR [mh Sunlight] OR season*:ti,ab OR winter:ti,ab OR spring:ti,ab OR autumn*:ti,ab OR summer:ti,ab OR "time of year":ti,ab OR sun:ti,ab OR sunlight:ti,ab OR sunshine:ti,ab) |
| Scopus | ("Pregnant Women" OR Pregnancy OR "Pregnancy Trimesters" OR "Pregnancy Complications" OR "Maternal Health Services" OR pregnan* OR maternal* OR "expectant mothers" OR gestational) AND ("Vitamin D" OR Ergocalciferols OR "Vitamin D Deficiency" OR "Vitamin D*" OR ergocalciferol*) AND (Seasons OR Sunlight OR season* OR winter OR spring OR autumn* OR summer OR "time of year" OR sun OR sunlight OR sunshine) |
| Article title | Authors | Publication year | Study design | Location of study | Sample size | Season of collection defined as | Vitamin D deficiency defined as |
|---|---|---|---|---|---|---|---|
| Vitamin D deficiency in adolescent pregnancy and obstetric outcomes | Öcal DF, Aycan Z, Dağdeviren G, Kanbur N, Küçüközkan T, Derman O | 2019 | Observational, cross-sectional | Turkey | n = 600 | Spring: Mar–May Summer: Jun–Aug Autumn: Sept–Nov Winter: Dec–Feb | < 20 ng/mL |
| Association between umbilical cord vitamin D levels and adverse neonatal outcomes | Treiber M, Mujezinović F, Pečovnik Balon B, Gorenjak M, Maver U, Dovnik A | 2020 | Prospective cohort | Slovenia | n = 400 | Summer: Sept Autumn: Dec Winter: Mar Spring: Jun | < 50 nmol/L |
| Maternal and neonatal vitamin D status at birth in black South Africans | Velaphi SC, Izu A, Madhi SA, Pettifor JM | 2019 | Prospective cohort | Johannesburg, South Africa | n = 291 | Summer: Dec–Feb Autumn: Mar–May Winter: Jun–Aug Spring: Sept–Nov | < 30 nmol/L |
| Vitamin D status in the first-trimester: Effects of vitamin D deficiency on pregnancy outcomes | Ates S, Sevket O, Ozcan P, Ozkal F, Kaya MO, Dane B | 2016 | Prospective observational | Turkey | n = 229 | Winter: Nov–April Summer: May–Oct | < 30 nmol/L |
| Human perinatal vitamin D metabolism. I. 25-Hydroxy-vitamin D in maternal and cord blood | Hillman LS, Haddad JG | 1974 | Prospective cohort | St. Louis, Missouri | n = 66 | N/A | N/A |
| Prevalence of vitamin D deficiency in the pregnant women: an observational study in Shanghai, China | Li H, Ma J, Huang R, Wen Y, Liu G, Xuan M, Yang L, Yang J, Song L | 2020 | Observational cohort | Shanghai, China | n = 34,417 | Spring: Mar– May Summer: Jun–Aug Autumn: Sept–Nov Winter: Dec–Feb | < 50 nmol/L |
| Determinants of maternal vitamin  D concentrations in Slovenia: A prospective observational study | Dovnik A, Mujezinović F, Treiber M, Pečovnik Balon B, Gorenjak M, Maver U, Takač I | 2017 | Prospective observational | Slovenia | n= 398 | Summer: Sept Autumn: Dec Winter: Mar Spring: Jun | < 50 nmol/L |
| Vitamin D status in Moroccan pregnant women and newborns: reports of 102 cases | Loudyi FM, Kassouati J, Kabiri M, Chahid N, Kharbach A, Aguenaou H, Barkat A | 2016 | Prospective observational, cross-sectional | Rabat, Morocco | n = 102 | Four seasons, undefined | < 50 nmol/L |
| High prevalence of hypovitaminosis D in pregnant Japanese women with threatened premature delivery | Shibata M, Suzuki A, Sekiya T, Sekiguchi S, Asano S, Udagawa Y, Itoh M | 2011 | Case-control | Tokai, Japan | n = 93 | Mar, Jun, Sept, Dec | < 20 nmol/L |
| Pregnancy in dark winters: implications for fetal bone growth? | Walsh JM, Kilbane M, McGowan CA, McKenna MJ, McAuliffe FM | 2013 | Prospective cohort | Dublin, Ireland | n = 60 | Winter: Sept/Oct Summer: Mar/Apr | < 30 ng/mL |
| High prevalence of vitamin D deficiency in pregnant Korean women: the first trimester and the winter season as risk factors for vitamin D deficiency | Choi R, Kim S, Yoo H, Cho YY, Kim SW, Chung JH, Oh SY, Lee SY | 2015 | Prospective cohort | South Korea | n = 220 | Four seasons, undefined | < 20 ng/mL |
| Study type | Article ID | Authors/publication year | MMAT question number | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Quantitative descriptive | S1 | S2 | 4.1 | 4.2 | 4.3 | 4.4 | 4.5 | ||
| Observational studies | 1 | Öcal et al (2019) | Y | Y | Y | Y | Y | N | Y |
| 8 | Loudyi et al (2016) | Y | Y | Y | N | Y | N | Y | |
| 9 | Shibata et al (2011) | Y | Y | N | N | Y | N | Y | |
| Quantitative non-randomized studies | S1 | S2 | 3.1 | 3.2 | 3.3 | 3.4 | 3.5 | ||
| 2 | Teriber et al (2020) | Y | Y | Y | Y | Y | Y | Y | |
| 3 | Velaphi et al (2019) | Y | Y | Y | Y | Y | N | Y | |
| 4 | Ates et al (2016) | Y | Y | Y | Y | Y | Y | Y | |
| 5 | Hillman & Haddad (1974) | Y | Y | N | Y | Y | N | Y | |
| 6 | Li et al (2020) | Y | Y | Y | Y | Y | N | Y | |
| 7 | Dovnik et al (2017) | Y | Y | Y | Y | Y | Y | Y | |
| 10 | Walsh et al (2013) | Y | Y | N | Y | Y | N | Y | |
| 11 | Choi et al (2015) | Y | Y | N | Y | Y | Y | Y | |
| Statistically significant results? | |||||
|---|---|---|---|---|---|
| Seasonal variation in vitamin D | Preterm birth | Birth weight | Birth length | Head circumference | |
| aOnly between some seasons (Choi: not between winter/spring and summer/fall) (Hillman & Haddad: only significant in Dec/Jan). bWeak correlation between maternal levels and weight but did not hold up with maternal-cord differences. | |||||
| Öcal et al (2019) | Yes | Yes | Yes | — | — |
| Treiber et al (2020) | No | Yes | No | No | No |
| Velaphi et al (2019) | Yes | No | No | — | — |
| Ates et al (2016) | Yes | No | No | — | — |
| Hillman & Haddad (1974) | Yesa | No | Yesb | — | — |
| Li et al (2020) | Yes | — | No | — | — |
| Dovnik et al (2017) | Yes | Yes | — | — | — |
| Loudyi et al (2016) | No | — | No | — | — |
| Shibata et al (2011) | No | Yes | — | — | — |
| Walsh et al (2013) | Yes | — | No | No | No |
| Choi et al (2015) | Yesa | No | No | — | — |