Independent variables
The main independent variables were the mode of conception (spontaneous
/ IVF/ICSI) in the observational study, and infertility with
reproductive surgery in the case-control study (yes / no).
Independent co-variables were maternal age (continuous), maternal age at
delivery >35 years, pre-pregnancy body mass index (BMI)
(continuous), BMI ≥ 30 kg/m2 (yes / no), BMI < 18.5 kg/m2 (yes
/ no), gestational weight gain (GWG) z-score (continuous), GWG z-score
> -2 (yes / no), GWG z-score > 2 (yes / no),
pre-pregnancy hypertension (yes / no), pre-pregnancy diabetes (yes /
no), previous conization (yes / no), uterine anomalies (yes / no),
chronic kidney disease (yes / no), other chronic diseases (heart,
thyroid and/or mental disease) (yes / no), previous preterm delivery
(yes / no), previous miscarriage (yes / no), smoking (yes / no),
preeclampsia/eclampsia (yes / no), gestational diabetes (yes / no),
small-for-gestational age neonate (birthweight < 10th
percentile) (yes / no), nulliparous (yes / no).
BMI was defined as the woman’s body mass divided by the square of body
stature (kg/m2). The pre-gravid BMI was categorized according to the
Institute of Medicine criteria as underweight (< 18.5 kg/m2),
normal weight (18.5–24.9 kg/m2), and overweight (15.0-29.9 9 kg/m2),
and obese (≥ 30 kg/m2)12. In Slovenia, maternal weight
is recorded at the first appointment in pregnancy and all appointments
after. The mean gestational week at the first appointment in pregnancy
was nine weeks. For the calculation of the GWG z-score, we used the same
method as described before13. Preeclampsia was defined
as the presence of hypertension (blood pressure ≥ 140 and/or 90 mmHg)
and any other end-organ dysfunction after the 20th week of
gestation14. National guidelines for screening and
diagnosing GDM changed during the study period. Until 2012, GDM was
diagnosed in Slovenia using the two-step approach: screening with 50 g
oral glucose load and, when indicated, performing a 100 g oral glucose
tolerance test (OGTT) using the Carpenter and Coustan
criteria15. Since 2012, we diagnose GDM using the
one-step approach by a 75-g OGTT according to the 2010 International
Association of Diabetes and Pregnancy Study Groups
Consensus16. SGA was a neonate with birthweight below
the 10th percentile for gestational age and gender-based on a Slovenian
Birth Weight Standards17. A nulliparous woman was
defined as a pregnant woman who had no previous viable pregnancies.