Anterior rotation in occiput transverse and occiput posterior positions

Abstract

Objective To investigate the natural rotation of the fetal head during labor when it was engaged by occiput transverse (OT) or occiput posterior(OP) positions. Methods A total of 1 013 parturients was included who had a singleton term gestation, vertex presentation, OT or OP position with cervical dilatation of ≤ 3 cm, and vaginal delivery. All parturients were delivered in Xiamen Hospital of Traditional Chinese Medicine during April 1 to December 31, 2014. Cervical dilation, station, and fetal position of every delivery were systematically recorded. Main outcome was the cervical dilation and station of anterior rotation from OT or OP position. They were Stratified by cervical dilation every 2 cm since 4 cm into 4~5 cm, 6~7 cm, 8~9 cm, 10 cm; or were stratified by fetal head station every 1 cm since -2 (S-2) into S-1, S0, S+ 1, S+ 2, S+ 3. The differences in anterior rotation rate, dilatation, and head station between OT and OP were analyzed. Results There were 850 OT and 407 OP with cervical dilatation of ≤3 cm. The rate of anterior rotation was 82.5% (701/850) and 76.7% (312/407), respectively. The constituent ratio of OT rotating into occiput anterior position (OA) at different dilatation was different with that of OP (χ2=260.93, P<0.01) . The constituent ratio of OT rotating into OA at different fetal head station was different with that of OP (χ2=133.18, P<0.01). The cervical dilatation and fetal head station that make it easy for OT 's anterior rotation were 6~7 cm (OR=5.81 , 95% CI: 3.81~8.87), 8~9 cm(OR=4.99 , 95% CI: 3.19~7.83), and S+ 1(OR=3.01, 95% CI: 1.99~4.54), S+ 2(OR=5.43, 95% CI: 3.53~8.35). The cervical dilatation and fetal head station that make it easy for OP 's anterior rotation were 6~7 cm(OR=4.11, 95% CI: 2.24~7.89), 8~9 cm(OR=27.31, 95% CI: 15.12~49.34), 10 cm(OR=27.76 , 95% CI: 14.87~51.82), S+ 2(OR=4.84 , 95% CI: 3.03~7.73). Conclusions The anterior rotation time of OT is different from OP . It's easy for OT to rotate into OA when cervix dilate into 6~9 cm and fetal head station is at S+ 1~S+ 2. When cervix dilate into 6~10 cm and fetal head station is at S+ 2, it's easy for OP to rotate into OA. Key words: Labor, obstetric; ABNORMAL FETAL POSITIONS; Version, fetal