The aim of this study is to examine the associations between maternal BMI and levels of oxytocin in maternal plasma during augmentation with oxytocin during first stage of labor in term pregnancy.

A translational prospective experimental study in the delivery ward in Linköping. The study population will include women in two BMI groups (underweight/normal weight and overweight/obese) during first stage of labor with singleton full term pregnancy and cephalic presentation.The BMI is calculated from weight and height registered at the first antenatal visit around week 8-12. At the delivery ward, if the women are in need of labor augmentation with oxytocin infusion, a peripheral venous catheter will be placed in the contralateral arm from the arm where oxytocin will be administrated. The oxytocin infusion will be prepared to a concentration of 10 mU/ml and will be given according to a standardized protocol or to an infusion level giving maximum of 5 uterine contractions per 10 minutes. Blood samples for measuring plasma levels of oxytocin will be taken prior to start and before every increase in the rate of oxytocin infusion. The blood samples will be collected through the first stage of labor.

Inclusion Criteria:

Full-term pregnancy (from gestational week 37+0), singel pregnancy, vertex presentation, knowledge in the Swedish language, 18 years and older, known BMI, need of labor augmentation with oxytocin infusion during opening stage.

Exclusion Criteria:

Not participating in other studies at the delivery ward

Full-term pregnancy (from gestational week 37+0), singel pregnancy, vertex presentation, knowledge in the Swedish language, 18 years and older, known BMI, need of labor augmentation with oxytocin infusion during opening stage.

IPD will not be shared with other researchers