- Disproportion between size of normal fetal head to the pelvic diameters. It causes failure to progress in labor.
- Inlet contraction - ordinarily due to rickets early in life or an inherited small pelvis.
- narrowing of the anteroposterior diameter to less than 11 cm or a maximum transverse diameter of 12 cm or less.
- Assessment:
- When engagement does not occur in primigravidas (normally, it occurs at 36-38 weeks of pregnancy), suspect either a fetal head abnormality (larger than usual heads) or a pelvic abnormality (smaller than usual pelvis).
- All primis must have pelvic measurements before 24 weeks.
- Check trial labor - if the woman has a borderline inlet measurement, and the fetal lie and position are good, a trial labor may be allowed to see if labor may proceed normally. This may be continually allowed as long as there is progressing descent of presenting part and cervical dilatations.
- Management:
- closely monitor maternal and fetal well-being.
- emotional support, emphasize that trial labor is best for both mother and child.