Is your pelvis too narrow to accommodate your baby’s size during delivery?

Mother of two Nadiah Rasheed, 32, had always yearned for a natural birth. But despite doing a course on hypno-birthing and reading up everything she could on how to raise her chances of giving birth naturally, she ended up undergoing a C-section when she delivered both her children.

“For my older son, now 4, I had been in labour for 13 hours, and he was showing signs of distress, so the gynae said he had to come out by an emergency C-section,” Nadiah recalls. For her now 7-month-old daughter, she was hoping to do a VBAC (Vaginal birth after C-section), but her doctor advised her against it.

“My gynae said that even though I was quite tall at 1.69m, my pelvic structure is quite small, and it was unlikely that Rina (her daughter) would be able to go through,” she notes.

Both Nadiah’s babies were relatively big ― they weighed 3.45kg and 3.55kg at birth.

Cephalopelvic disproportion, or CPD, happens when the baby is too big for the expectant mum’s pelvis.

“It’s not a labour problem, but a delivery problem,” explains SmartParents expert obstetrician-gynaecologist Dr Christopher Chong.

It is one of the more common causes of an emergency C-section from a labouring mum, Dr Chong notes, though he adds that how common it is depends on how strict the doctor adheres to the definition.

“In some of these cases, the baby can even die under the doctor’s eyes. So, it’s important to recognise the problem before labour…”

“The head of the baby may not actually be large. At times, if the baby faces skywards, or if it has a hyperflexed* neck that causes the diameter of the head to be larger, it can make it hard to go through the pelvic bone passage, leading to CPD,” he points out.

What’s worse than CPD is shoulder dystocia, whereby after the head is delivered, the anterior shoulder of the infant cannot pass through. This can happen with large babies and diabetic mums, where “there can be extra deposition of fat around the trunk and shoulders of the foetus,” Dr Chong adds.

“In some of these cases, the baby can even die under the doctor’s eyes. So, it’s important to recognise the problem before labour and offer a C-section,” says Dr Chong. “About 10 per cent of C-sections are from CPD.”

*Extended beyond the normal range of motion.



Causes of CPD

Cephalopelvic disproportion can result from one or more of the following factors:

1. Baby is large
Your baby is considered big if she weighs 4kg or more at birth. The average weight of a baby is between 3 and 3.2kg. Several things can cause your baby to be larger than average: Genetics, eating too much during pregnancy, gestational diabetes, or if your baby is overdue. Boys are also generally larger than girls.

2. Pelvis is too small
Your pelvis may simply be too small to accommodate your baby. One study showed that shorter women were likely to have CPD. However, Dr Chong notes that it is usually not possible to determine CPD in advance, even though the doctor may discuss a C-section if the baby is large and the mummy is small. “Strictly speaking, CPD can only be diagnosed in labour ― when the cervix is opened fully, and the mum is unable to push the baby out.”

Dr Chong adds that many studies have been done to try to prevent patients from suffering a long labour which ends in a C-section. “These include measuring the pelvic bone diameters and scanning for the pelvic space ― but none of these showed any definite use.” In other words, the mum still has to go into labour and try, before knowing whether she will be successful in giving birth naturally.

3. Abnormal foetal position
One example is the occipito-posterior position ― where the baby is facing the mother’s abdomen instead of her back. Another instance is when the baby is in the “brow position” ― where her neck is hyperflexed and extended instead of her head being tucked down into her chin. In this position, the largest part of her head tries to fit into the pelvis first.

4. Abnormally shaped pelvis
“If there has been damage to the pelvic bone, such as in a road accident, then a C-section is the likely outcome,” says Dr Chong. Other reasons for an abnormally shaped pelvis could be diseases like rickets (a skeletal disorder that’s caused by a lack of vitamin D, calcium or phosphate), osteomalacia (softening of the bones due to a lack of vitamin D), or a tumour of the bones.

"Strictly speaking, CPD can only be diagnosed in labour ― when the cervix is opened fully, and the mum is unable to push the baby out.”

Dr Chong notes that experienced doctors can do a pelvic examination, consider the size of the foetus and counsel the mum on the possible birth outcome. “However, this is not fool-proof and is very individualised,” he points out.

The gynaecologist usually decides that a C-section is needed if the mum is unable to push the baby out after trying for a good period of time. “This time frame is not fixed, and depends on the judgement of the gynae,” Dr Chong says.

Even if labour has been going on 8 to 12 hours, the gynae would also consider whether the labour is progressing, whether the baby’s head is still high in the pelvis, and if the cervix is not dilating fully.

Subsequent pregnancies
For subsequent pregnancies, many mums who had CPD and a C-section in the first pregnancy would likely opt for repeat C-section. But Dr Chong says that studies show that up to 60 per cent of these mums were still able to have a normal vaginal delivery in subsequent pregnancies.

Although Dr Chong stresses that he does not recommend it, one of his patients did this: The mum gave birth to a big baby (3.6kg) via a C-section for her first pregnancy. For her next pregnancy, she dieted and went on to have a successful vaginal birth, delivering a 2.8kg baby.

Dr Chong notes, “Another option is to deliver early in full term, for example, once she has passed the 37 week mark, so the baby is not so big.”

Photos: iStock

Like us on Facebook and check SmartParents regularly for the latest reads!

You may also like…

What I wish I knew before I got pregnant…

Pain-relief for labour: What are your options?

9 pregnancy symptoms you should never ignore