The pelvis which supports the weight of the body through the spine; it is a bony cradle.

The baby’s head will move (engage) into the pelvis from roughly 36 weeks for a first baby
Any time up until, sometimes during labour for second and subsequent babies.
The baby’s head, shoulders and body need to pass through this circle of bone in order to be born.

Check out the Physiology of the Pelvis to remind yourself just how magical your pelvis is.

You will only grow a baby that is appropriate to you

Cephalopelvic disproportion (i.e. baby can’t fit) can happen in cases of injury, disease, malnutrition or gestational diabetes, but it is extremely unlikely.

Some of the things you hear women say because they have had it said to them … 

‘My last baby was far too big for me so I had to have a Caesarean’,

‘Thank goodness the obstetrician was there to save us, I would never have been able to get that baby out.’

More likely due to the circumstances of the births, such as position, choice of pain relief, intervention, etc. rather than a super-size baby.

In fact, several studies have shown it is the suspicion of a big baby, not big babies themselves that leads to complications because of the way women are subsequently treated (Decker and Bertone, 2019) It is also impossible to tell the internal proportions of a woman’s pelvis by looking at her. 

Petite women can and do give birth to 10lb baby’s without so much as a graze! The fact of the matter is, our babies are far more likely to weigh upwards of 7-8lbs than under. Our babies are getting bigger because we are.
If you have visited heritage buildings you may have noticed that some of the doorways were low because the people were smaller.