Background/Objectives: Vitamin D deficiency has been associated with an increased risk of adverse perinatal outcomes (APOs). This study aimed to examine whether vitamin D deficiency during the first trimester of pregnancy is linked to the development of gestational diabetes mellitus (GDM) in a Mexican population. Methods: A total of 404 pregnant women from the Biochemical and Epigenetic Origin of Overweight and Obesity (OBESO) cohort were included. Maternal vitamin D levels were measured between 11 and 14 weeks of gestation. Vitamin D deficiency was defined as a level below 20.0 ng/mL. The primary goal was to compare APOs between Group 1 (women with vitamin D deficiency) and Group 2 (women without vitamin D deficiency). Adjusted odds ratio (aOR) for APOs—including GDM, preeclampsia, preterm birth, miscarriage, cesarean section, and neonatal size—were calculated, adjusting for pregestational body mass index (BMI) and obesity, with 95% confidence interval (95% CI). Results: Vitamin D deficiency was present in 40.5% of women. Pre-pregnancy BMI and obesity were significantly higher in women with deficiency; other baseline characteristics did not differ between groups. Women with vitamin D deficiency had a higher risk of GDM (aOR 2.04, 95% CI 1.14–3.65, p = 0.01). No association was found between vitamin D deficiency and other APOs. Conclusions: The incidence of vitamin D deficiency in the first trimester was 40.5%. Early pregnancy vitamin D deficiency increases the risk of GDM among Mexican women. These findings highlight the importance of monitoring and supplementing vitamin D during pregnancy to reduce the risk of GDM.

Background/Objectives: Myomectomy is the preferred treatment for women with uterine fibroids who desire to preserve their fertility. This study aimed to compare perinatal outcomes between Mexican women with and without a history of myomectomy, matched in a 1:2 ratio based on maternal age and parity. Methods: A retrospective cohort study was conducted involving women with and without a history of myomectomy who received prenatal care and delivered at a tertiary care hospital in Mexico City. Women with comorbidities such as pregestational diabetes, chronic hypertension, autoimmune diseases, nephropathy, cardiomyopathy, and cancer were excluded from the study. Group 1 consisted of women with a history of myomectomy, and Group 2 included matched women without such a history. The following perinatal outcomes were evaluated: miscarriage, preterm birth, cesarean section, obstetric hemorrhage, placenta previa, surgical adhesions, and obstetric hysterectomy. Adjusted relative risk (aRR) with 95% confidence intervals (CI) was calculated. Results: A total of 122 women were analyzed in group 1, and 244 in group 2. The risk of obstetric hemorrhage aRR 7.5 (95% CI 3.9–11.9), surgical adhesions aRR 11.8 (5.3–20.7), and placenta accreta aRR 15.3 (1.3–111) were significantly higher in Group 1 compared to Group 2. Other outcomes, including miscarriage, preterm birth, cesarean section, placenta previa, and obstetric hysterectomy, were similar between groups. Conclusions: Mexican pregnant women with a history of myomectomy have a higher risk of obstetric hemorrhage, surgical adhesions, and placenta accreta compared to those without such a history.