The Association Of Vitamin D,Parathyroid Hormone In The Second Trimester And Offspring Birth Weight

ObjectiveDescribe the status of vitamin D?VD?and parathyroid hormone?PTH?in pregnant women during the second trimester of Hefei,Anhui.And Provide a basis for preventing fetal growth restriction during pregnancy.MethodsFrom May 2015 to December 2017,4768 pregnancies for 14 to 27 weeks,singleton pregnancy,long-term residence in Hefei and without serious illness before pregnancy was recruited from Hefei First People's Hospital,Hefei Maternal and Child Health Hospital and the First Affiliated Hospital of Anhui Medical University.All the subjects were enrolled in the second trimester and finished the Hefei Pregnancy Mid-Medical Health Questionnaires,which was given a fasting venous blood sample during early morning,followed up to delivery,and the birth outcome information was obtained from the medical records.Pregnancies with severe pregnancy complications?cardiac dysfunction,moderate or severe eclampsia,thyroid system diseases and severe anemia,et al.?,multiple pregnancies,artificial assisted reproduction,and loss of follow-up?no birth outcome information?were excluded,and 3407 pregnant women were eventually included as subjects.All 3407 subjects were tested for 25?OH?D,1703samples were randomly selected to detect PTH and they were determined by chemiluminescence method.The degree of VD deficiency is recommended by the NationalAcademyofSciencesInstituteofMedicine,VDdeficiency?25?OH?D<50nmol/L?,mild deficiency?30 nmol/L?25?OH?D<50 nmol/L?and severe deficiency?25?OH?D<30 nmol/L?;the level of PTH is divided into two groups,high-level PTH group(?P₇₅)and low-level PTH group(<P₇₅).Univariate analysis of factors affecting VD and PTH levels and birth weight was performed using a 2-test and analysis of variance.A multivariate linear regression model was used to analyze the effects of a single VD and PTH subgroup on the birth weight and the interaction between them and the birth weight.Results Among the 3407 pregnancies in the second trimester,they were divided into three groups according to the degree of vitamin D deficiency,the severe vitamin D deficiency?25?OH?D<30nmol/L?,the mild vitamin D deficiency?30nmol/L?25?OH?D<50nmol/L?and the non-deficiency?25?OH?D>50 nmol/L?,accounting for 29.4%,46.9%and 23.7%of pregnancies,respectively.The level of PTH was divided into two groups according to the quartile array,high-level PTH group(?P₇₅)and low-level PTH group(<P₇₅).The P₇₅5 concentration of PTH in pregnant women was 16.7 ng/L,and the average levels of 25?OH?D and PTH were?39.9±16.3?nmol/L and?12.9±7.6?ng/L,respectively.The mean birth weight was?3402.4±397.6?g.Factors affecting 25?OH?D levels include family income,blood collection season,pre-pregnancy BMI,total weight gain,number of calcium tablets taken after pregnancy,cod liver oil in the past week,multivitamins,number of milk consumed in the past week,and sun exposure time;PTH level The influencing factors include maternal age,parity,gestational age,blood collection season,the number of calcium tablets taken after pregnancy,freshwater fish,milk and sun exposure time in the past week.There was a negative correlation between 25?OH?D and PTH levels in the second trimester?r=-0.068,P=0.008?.As the degree of VD deficiency decreased,PTH levels decreased significantly??=-0.77ng/L,95%CI:-1.26,-0.28?,the risk of high-level PTH(PTH?P₇₅)was significantly reduced?RR=0.78,95%CI:0.66,0.91?.According to the multivariate analysis of independently vitamin D and PTH levels in the second trimester with birth weight and the risk of SGA,we found that as the vitamin D non-deficiency pregnancies as the reference group,the birth weight of the mild vitamin D deficiency group was significantly decreased by-46.7?95%CI:-88.6,-4.7?g;The severe vitamin D deficiency group had a significant decrease in birth weight of 76.4?95%CI:-124.1,-28.7?g and the risk of SGA increased significantly by2.21?95%CI:1.21,4.05?times.Compared with the low-level PTH group as the reference group,the birth weight of the high-level PTH group decreased significantly by 38.9?95%CI:-77.1,-0.5?g.The multivariate analysis of the interaction between vitamin D and PTH levels in the second trimester with birth weight and the risk of SGA,we divided pregnancies into 6groups according to the vitamin D deficiency status and PTH level.Compared with PTH<P₇₅5 and 25?OH??50nmol/L group,the fetal birth weight of maternal 30 nmol/L?25?OH?D<50 nmol/L with PTH<P₇₅5 or PTH?P₇₅5 pregnancies decreased significantly by 52.9g?95%CI:-99.5,-6.1?and 95.9g?95%CI:-157.1,-34.8?,and the risk of SGA increased significantly by 1.92?95%CI:1.02,3.64?and 2.28?95%CI:1.04,4.98?times.The birth weight of pregnancies with maternal 25?OH?D<30nmol/L coexisting PTH<P₇₅5 or PTH?P₇₅5 group decreased significantly by 80.3g?95%CI:-133.8,-26.9?and 127.8g?95%CI:-197.2,-58.3?,respectively,and the risk of SGA increased significantly by 2.54?95%CI:1.26,5.10?and 3.19?95%CI:1.36,7.48?times.It is evident that the severe vitamin D deficiency with elevated PTH group(25?OH?D<30nmol/L with PTH?P₇₅)have the highest birth weight loss and the highest risk of SGA.In addition,the severe vitamin D deficiency with elevated PTH group had the highest calcium level during pregnancy?1.540±0.193?mol/L?and the risk of low calcium intake?<3 times/w?was highest?RR=4.05,95%CI:2.48,6.61?.Conclusions In this study,the pregnancies had a high rate of VD deficiency.The VD deficiency in the second trimester is associated with decreased neonatal birth weight,especially in severe deficiency pregnancies.The increase in PTH during the second trimester is an independent risk factor for the reduction of birth weight.Elevated PTH induced would further aggravate risk of offspring birth weight developmental restriction for pregnancies with severe VDD through impaired maternal calcium metabolism homeostasis.