Development of the human reproductive system begins toward the end of the first trimester; studies have shown its sensitivity to environmental chemicals, especially EDCs.
Fetal cells can be safely obtained from amniotic fluid (AF), chorionic villus sampling (CVS) or cordocentesis (CB) and can be used for precise and accurate prenatal diagnosis [ 5]. Second trimester studies of AF are performed at about 16 weeks' of gestation without significant technical difficulties.
Second-trimester studies on uterine artery Doppler in twins confirm lower PI values during the course of the pregnancy, which decrease with advancing gestational age.
In a previous publication by our group we provided an overview of all first-trimester studies that used metabolomics techniques in maternal blood for the early prediction of PE [ 8].
a The number of pregnancy trimesters studied is shown into parenthesis The region under study is subject to important climatic variations during the year, with average air ambient temperature ranging from -15°C to + 24°C and different lengths of seasons (i.e., long winters and relatively short summers).
Maternal smoking does not appear to alter fetal testosterone levels, however, during the second trimester (this study and Fowler et al., 2008) and so smoke-induced changes in AGD appear unlikely to be due to direct changes in androgen levels.
Ten studies were performed in the first trimester, 32 studies at a mean gestation between 15 to 20 weeks and two studies 20 to 24 weeks.
In their meta-analysis, Sapkota et al. (2010) estimated the association between LBW and maternal PM10 exposure during the first trimester (five studies) and third trimester (seven studies), but did not detect associations with exposure in either trimester (OR = 1.00; 95% CI: 0.97, 1.03, and OR = 1.00; 95% CI: 0.99, 1.01, respectively).
Although the rates for total miscarriages (10 studies; 4.6% v 2.8%, 1.04, 0.90 to 1.21) and miscarriage in the first trimester (four studies; 9.8% v 8.4%, 1.16, 0.80 to 1.69) was similar for treated and untreated women, cervical treatment was associated with a significantly increased risk of miscarriage in the second trimester.
Thus the possible fetal growth promoting and/or preterm birth reducing effect of vitamin supplements in the second and mainly in the third trimester was studied.
"Time" is an indicator of time and covers the 9 trimesters of study (variable coded 1 9).
