Estimating the impact of pelvic immaturity and young maternal age on fetal malposition

Fetal malposition, specifically occiput posterior and transverse (OP/OT), is associated with higher intra-partum morbidity. We tested the hypothesis that young maternal age and pelvic immaturity are risk factors for fetal malposition.

In a cohort study of all nulliparous teen (≤18 years) deliveries over a 4-year period at one institution, fetal head position at time of delivery was collected and correlated with maternal characteristics and outcome data. Using Risser staging observations, pelvic maturity age was set at 16, and accordingly, the women were divided into two groups (younger vs. older teens). Analysis was performed using Fisher's exact, student t test, and logistic regression modeling.

Older teen mothers (16-18 years, n = 609) had higher rates of malposition (22 vs. 12 %, p = 0.02) when compared with younger teens (≤15 years, n = 98). Among all women with a malpositioned fetus, older teens had a higher body mass index (BMI: 32.6 ± 6.7 vs. 28.5 ± 3.5, p = 0.04) and subsequent need for cesarean delivery (69 vs. 33 %, p = 0.02) when compared with their younger counterparts. Although younger teens were more successful in having a vaginal delivery (67 %) with an OP/OT position, it was at the expense of a 25 % rate of severe perineal laceration (third/fourth degree).

Obesity, and not young maternal age or pelvic immaturity, is associated with fetal malposition. The direct association with increasing pre-pregnancy BMI and the long-term impacts of the high rates of cesarean delivery in this young population underscores the need for more public health focus.