Fetal Head Engagement: A First-Time Mother's Experience & Concerns

Question
I am 34 years old and expecting my first child after diagnosed fertility problems. LMP was definitely 2/4/04 and I am due between 7/1/05 - 11/1/05 according to the u/s done at 6 weeks. Over the last few months there has been suspicion about the large size of my baby from the various indicators noted by the practitioners I have seen. Finally at my 39 week appointment I was informed that the baby's head was firmly fixed and immobile at the pelvic brim, but only one fifths into the brim as four fifths could still be felt above the brim. The midwife suggested the baby has a very large head and although fundal height isn't used routinely at this late stage it was recorded as 42cm. It has always been well ahead of what is expected and my fluid levels are perfectly in the middle of the average range. My question is if the baby's head is firmly immobile already and only one fifth engaged, does this suggest it may be too big for the pelvis or is there still a large chance it will engage further in the next week or so prior to the start of labour? I thought that it doesn't become firmly immobile until it is further engaged into the pelvis. I understand that it may engage further as labour starts with the release of hormones, widening the space and that is why a trial of labour is recommended before any decisions are made about c/sections.

Answer
Based on your LMP, you are due on January 11, and are now 39 weeks 1 day. If you believe that the baby appears large, you can have a sonogram done now (a biophyccal profile) and get an estimated fetal weight (EFW). ACOG (American College of ObGyn) recommends that, if the EFW is greater than 9.5lbs, we should give the patient the option of having an elective cesarean section. If it is less than 9.5lbs, you can attempt a trial of labor. The baby does not usually become fully engaged until you are in labor. Don't worry about the subjective size of the baby's head. Give it a chance in a trial of labor. Your midwife or doctor will know more after you are in active labor. When you start to have contractions every 3 minutes (from the beginning of one contraction to the beginning of the next contraction) at the level of your belly button, and each contraction lasts (remains hard) for,at least, 45 seconds, and this continues for a full hour, we consider you to be in labor. If you are dilated more than 3-4 cm, you will be admitted to the hospital. Once you dilate up to 5cm, you should continue to dilate at the rate of 1cm/hour. If you don't, and the baby appears large, you will be offered the option of a cesarean. If you do get to full dilatation (10cm) you will be allowed to push for 2 hours. If there is no progress, you will have to deliver by cesarean section. Of course, if there are any problems with the fetal tracing or heartbeat at any time in the labor, a cesarean section will be done to get the baby out in the most appropriate manner. Good Luck.