The last month of pregnancy is often the most difficult. By now your baby is fully grown and taking up every inch of available space, which may put strain on your ribs, back and pelvis.
Fortunately it’s also the time when your baby’s head engages (fits) into the top of the pelvic brim to begin its journey into, through and finally out of the pelvis during birth. The little notches of this bumpy, bony structure actually direct the baby’s head into the right positions throughout this journey.
Sometimes the woman’s pelvis is not the right shape or size, or has been damaged in an accident, and this can necessitate a caesarean birth.
What happens when baby engages?
To make a model pelvis, put your two hands together with fingertips touching. Your thumbs are your pubic bone, your index and middle fingers your back or sacrum, and your pinkies are where your coccyx would be.
Now take a tennis ball (this is your baby’s head) put it into the top (this is your baby’s head engaging) and notice how the ball curves down, around and out. This is what happens during the final month of your pregnancy when your baby’s head engages.
When should baby engage?
If this is your first baby, the head should start to engage at least four weeks before your due date. Pregnancy hormones relaxin and progesterone softens connective tissue around the pelvic joints in preparation for this. In subsequent pregnancies, the baby’s head can engage later in the pregnancy – sometimes only a week before labour.
Also read: Is your pelvis big enough for labour?
How will I know when this happens?
You will look and feel different when your baby’s head engages. People will notice the change and say things like "You've dropped!" or "Your baby is very low, you are going to go into labour soon.”
One benefit is that you will be able to breathe easier – the top of your womb no longer feels as though it’s under your chin. But you may feel uncomfortable if you sit for too long in the same position and hard as you try not to, your walk will become a duck waddle. Other discomforts include backache and stronger Braxton Hicks (false labour).
What happens if baby engages too soon or does not engage at all?
Women who have had frequent pregnancies in a short space of time or women carrying a small or breech baby may notice that her baby engages very early. This could be a warning that your baby may be born prematurely.
If the baby’s head is not engaging at all, it may be because the woman’s pelvis is too small (often with teenage pregnancies) or the baby is too big. When this happens it’s called cephalopelvic disproportion (CPD). It can also happen that the baby’s head does not engage even though there is no sign of CPD.
The doctor may suspect that the placenta is low-lying and blocking the baby’s passage. When placenta praevia is
diagnosed, natural birth (depending on the degree of praevia) should be tried with caution or not be attempted.
When the baby is lying in breech (bottom first) or transverse (arm first), engaging will not be optimal and vaginal birth shouldn’t be attempted. If your baby has not engaged by 38 weeks, it doesn’t always mean there is a problem. Some only engage once labour starts and a trial of labour is possible if both mom and baby are healthy