Introduction:
The presence of abnormal body weight before pregnancy and in the first trimester of pregnancy is a crucial risk factor of preterm birth (PTB) and low birth weight (LBW)¹. The global preterm birth rate has remained constant for over 20 years, amounting to 9.6–11%^2-4. On the other hand, data from the World Health Organization (WHO) show that in recent years an increase in the number of premature births has been observed in many countries (mainly in industrialized countries). Prematurity and low birth weight is one of the most important and still valid challenges of modern medicine, which is also a socio-economic problem. Preterm babies require interdisciplinary, specialist treatment, diagnostics and rehabilitation, sometimes lasting their entire life. Literature data show that approximately 15 million premature babies are born in the world each year^2,5,6. In many studies researchers mentioned that abnormal pre-pregnancy BMI is a very important independent risk factor of PTB. This value also determines the recommended maternity weight gain during pregnancy. The data obtained in this way are considered the most important indicators of the nutritional status of a pregnant woman⁷. Abnormal BMI is also associated with an increased risk of gestational diabetes, pre-eclampsia and eclampsia, pregnancy-induced hypertension (PIH) and other perinatal abnormalities^1,8,9. The consequences of the increase in the frequency of premature childbirths and low birth weight lead to a critical analysis of the factors that may affect their occurrence and effects (social, medical, psychological and economic). The aim of this study was to assess how pre-pregnancy BMI and inappropriate gestational weight gain are associated with preterm birth, low birth weight and type of birth.

Material and Methods:
We conducted a retrospective cross-sectional study of 394 Polish women in the postpartum period. We used a questionnaire with the structure of the medical interview. To analyze factors related to birth outcomes, we used the Pearson's Chi^2 test of independence and odds ratio (OR), with a corresponding 95% confidence interval (CI), followed by a multiple logistic regression.

Results:
The pre-pregnancy BMI affects the way of pregnancy termination - in the group of women with a higher BMI there were more cesarean sections. Pre-pregnancy BMI also influenced the week of pregnancy termi-nation, i.e. incorrect BMI contributed to an increase in the percentage of premature births. 25% women with normal weight [BMI 18.5 to 24.9] had EWG, excessive gestational weight gain, 40 % had AWG, appropriate weight gain, and 35 % LWG, too little weight gain (rec-ommended WG 11.5–16.0 kg); women with overweight and obesity [ BMI 25.0 to <30] had EWG in 62%, AWG in 21% and LWG in 17% (recommended WG 7.0–11.5 kg); women with underweight [>18.5] had EWG in 6%, AWG in 67% and LWG in 28% (recommended WG 12.5-18.0 kg). Inappropriate gestational weight gain affects of category of pregnancy termination and category of newborn’s birth weight (p<0,0001).

Conclusions:
The pre-pregnancy BMI affects the way of pregnancy termination - in the group of women with a higher BMI there were more cesarean sections. Pre-pregnancy BMI also influenced the week of pregnancy termination, i.e. incorrect BMI contributed to an increase in the percentage of premature births. Our findings indicate that promoting weight management remains a priority in public health policy, and women of childbearing age should be encouraged to adopt or maintain healthy lifestyle during pregnancy in order to avoid sed-entary - and obesity-associated risks affecting birth and newborns' health. Our study suggests that appropriate gestational weight gain recommendations to prevent perinatal complications.