The Relationship between First Trimester 25-Hydroxyvitamin D3 Levels and Second Trimester Femur Length and their Effects on Birth Weight and Length at Birth

Introduction

Vitamin D is important for fetal development because of its important role during cell proliferation, differentiation, and maturation processes [1,2], also vitamin D is important for placental function, calcium homeostasis, and bone mineralization, which are all important determinants for fetal growth and development [3,4]. Primary source of vitamin D is the exposure to sunlight. Sedentary indoor lifestyles, obesity, and avoiding sunlight each contributes to increased vitamin D deficiency. A pregnant woman needs a daily intake of vitamin D of 800–1000 IU, but the actual need varies according to ethnicity, nutritional factors, and sunlight exposure [5]. Vitamin D deficiency in pregnant women is a great public health problem because of its potential effects on the maternal obstetric outcomes and offspring development [6,7] where vitamin D deficiency may affect early organogenesis and subsequently affect later health and disease [8]. Vitamin D deficiency during pregnancy has been associated with increased risk of adverse obstetric outcomes including increased risk of gestational diabetes, pre-eclampsia, threatened preterm birth, cesarean section, bacterial vaginosis [9-11], also may have adverse effects on fetal development and growth include increase risk of preterm birth and fetal growth restriction resulting in low birthweight and small for-gestational-age neonates [12,13]. It has also been shown that intrauterine bone hypo mineralization is associated with vitamin D deficiency and then a reason for congenital rickets, craniotabes, and osteopenia [14]. 25hydroxy vitamin D is the major storage form of vitamin D in the human, so it can be measured in blood to determine the overall vitamin D status [15], it is the best measure of vitamin D status in human [16]. The main goal of our study was to assess the relationship between maternal circulating 25-hydroxyvitamin D3 [25(OH)D3] concentration and second trimester femur length, infant birthweight and length at birth.

Materials and Methods

A prospective study was conducted in El Shatby Maternity University Hospital, Alexandria, Egypt during the period from December 2019 to November 2020 on 300 pregnant women in the antenatal care clinic during their first antenatal visit between (10–13 weeks of gestation). Inclusion criteria were: 20-35 years of age, singleton alive normal pregnancy, between 10 and 14 weeks of pregnancy as confirmed by ultrasonography at recruitment, and most nutritional status as defined by pre-pregnancy body mass index was within normal value. Exclusion criteria were Multiple pregnancies, pregnancies with previously known metabolic disorders, Chronic disease and tumor, chronic debilitating diseases, obesity pregnant women take corticosteroids, drug abuse (including alcohol) and if the pregnant women during the first trimester of the current pregnancy suffered from severe infections, trauma or operation. All the women who fitted for the study were asked to participate in the study after explaining the details of the study and the importance of their follow up then written consent was obtained. Each participant was interviewed for demographic data, complete history taking, obstetric history, past history, medical history and knowledge on nutrition support in pregnancy. Ultrasound was done during the initial visit to measure the Crown-rump length and confirming that the women in the first trimester of pregnancy then a single maternal blood samples was collected in 12th to 14th weeks to measure 25-hydroxyvitamin D3, and were determined in all women. Second trimester femur length was measured in all cases, and the women were followed until the birth. The birth outcomes were weight in grams and birth length in centimeters. The circulating concentration of 25(OH)D3 in pregnant women was measured in the first trimester and the women were categorized into three groups according to its level: deficiency level <20 ng/ml, insufficiency level 20–29.99 ng/ml, and sufficiency level >30 ng/ml [17,18].

Results

300 pregnant women were enrolled in the study, they were classified into three groups according to their first trimester serum vitamin D level. Group A(n=160) deficient group was comprised of serum vitamin D levels less than 20 ng/ml, group B (n=84) insufficient group was comprised of serum vitamin D levels between20-29.99 ng/ ml and group C(n=56) sufficient group where vitamin D level >30 ng/ ml. Results. Table 1 showed that Serum 25(OH)D was deficient (less than 20ng/ml) in 53.3% (n = 160) which is group A while 28% (n = 84) of pregnant women had insufficient level between(20-29.9ng/ml) (group B) and 18.7%(n=56) had sufficient level (more than 30ng/ml) in group C. There were only 18.7% (56 of 300) had serum 25(OH) more than 30ng/ml which means higher prevalence of low level of vitamin D in pregnant women. There were no significant differences between three groups as regard patient age, gestational age in the first trimester and pre-pregnancy body mass index. There were differences in second trimester femur length and birth height with significant difference but there was no difference in birth weight among the three groups.

  

    
  
    
Group    A 
    
Group    B 
    
Group    C 
    
P    value 
  
  

    
n=160 
    
n=84 
    
n=56 
  
  

    
25(OH)D level 
    
14.49±2.30 
    
22.76±3.68 
    
33.77±4.2 
    
  
  
  

    
Incidence of 25(OH)D 
    
53.30% 
    
28% 
    
18.70% 
  
  

    
Patient age 
    
28.2±3.5 
    
28.3±3.7 
    
29.4±2.6 
    
  
  
  

    
Pre-pregnancy BMI 
    
23.28±3.52 
    
23.33±3.50 
    
23.64±3.54 
    
  
  
  

    
Gestational age(10-14 wk) 
    
11.2±4 
    
12.4±2 
    
11.4±3 
    
  
  
  

    
2nd trimester Fl(mm) 
    
33.5±1.3 
    
35.3±8.2 
    
35.96±7.4 
    
0.034 
  
  

    
Birth weight (kg) 
    
3490±0.323 
    
3569.45 
    
3572.44 
    
0.067 
  
  

    
Birth height(cm) 
    
50.4±2.9 
    
50.5±2.3 
    
50.7±3.7 
    
0.039 
  

Table 1: Birth weight among the three groups.