Most first-time mums worry about how an entire human baby is going to come out of their tiny lady bits, but for those who are petite or carrying gigantic babies, the fear is real. What to do if the baby is too big becomes a real concern, and here are all the facts when it comes to birthing babies when you have a small pelvis and/or a big baby.
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Is Pelvis too Puny?
The term ‘cephalopelvic disproportion’ (also known as CPD) refers to when a woman’s pelvis is simply too small for their baby’s head to pass through.
While it is a real condition, it’s extremely rare and mostly occurred in previous centuries when poor nutrition and illnesses like polio caused women to have pelvic anomalies. Thankfully, almost all women these days have a pelvis that will adjust to allow the baby to move safely through the birth canal; the only exceptions might be if you have a pelvic injury or congenital abnormality.
Other true cases of CPD are very few and far between and can only be diagnosed once labour has started. However, misdiagnosis is common too (when labour is taking longer than expected), which is perhaps why people believe CPD occurs more often than it does.
Moving Objects
While you might be bewildered about how your big baby is going to fit, you have to remember that the human body is incredible and both your pelvis and a baby’s head are designed to move in a way that makes the birthing process possible.
For starters, your pelvis is made up of several different bones held in place by ligaments, and when pregnant, your body releases the hormone ‘relaxin which loosens your pelvic joints and ligaments in preparation for labour.
Unlike an adult’s skull, your baby’s head is also made up of several bones that aren’t yet fused, which means it’s malleable and can change shape to fit through the birth canal. A baby’s skull bones don’t connect and strengthen until a little while after they’re born, which is why newborns have those soft spots called fontanelles (the membranous gaps between the bones).
Where’s Your Baby At?
For a baby to descend and travel through the birth canal and into the world, they ideally need to be in the right position to begin with, which is head down. When babies are facing the other way, it’s called a breech position. While most babies will turn around in the final weeks or days before labour starts, some don’t, which can make birth quite difficult.
A vaginal breech delivery is not impossible, but it is considered riskier for a baby to be delivered feet first, and a lot harder for the mother.
If a baby is breech, often doctors will try methods to turn the baby, such as using their hands in a procedure called the ‘external cephalic version’ (ECV). Otherwise, they may recommend a C-section delivery.
In all of these cases, the issue is the position of the baby, and NOT because the mother has a pelvis that’s too small.
Widening the Gap
If your baby isn’t breech and you’re going for a vaginal delivery, you can help create more room for your baby during labor, depending on your birthing position. Lying flat on your back or even a bit reclined is the preferred norm for a lot of women and doctors. However, this can narrow your pelvis by 30 percent, which is not what you want at all!
The best positions to help widen the gap (so to speak), and help your baby travel down the birth canal are squatting, on all fours, or lying on your side.
Bigger Than They Seem
You may think that your baby bump is huge, or perhaps your doctor has estimated you’re carrying a big one, but it’s important to remember two things. The first is that all women carry babies differently. Some look huge and have average-sized babies, and some look tiny and have whoppers. The size of your bump doesn’t necessarily determine the size of your baby.
The second thing to know is that doctors can only estimate with ultrasound measurements; there isn’t an accurate way to predict the size and weight of a baby before birth, so often they may be smaller (or bigger) than what’s anticipated.
You Can Do This!
If your baby isn’t breech and you’re keen for a vaginal birth, but you’re terrified that your baby isn’t going to fit, relax and remember that your body is designed to make it happen. Your baby WILL fit! It can just take a bit longer for some babies than others.
And of course, in the event of an emergency, the doctors are on hand to assist with forceps or perform an emergency c-section if required, making sure you and your bub are safe.
Are You Worried About a Large Baby? Birth Weight: Four Things You Should Know
When my patients reach the final weeks of their pregnancy, they often start asking about how much their baby will be and what this means for delivery.
Even doctors think about it. We want to know the exact weight of the baby to make the best birth plan. Predicting birth weight can be very difficult.
In a study conducted recently, one-third of women said their OB told them that their baby was getting “quite big” towards the end of their pregnancy. Only one-fifth of these women ended up with a baby that was heavier than 8 pounds 13 ounces, or 4000 grams. This is the common threshold to label a child “large.”
If we knew the exact weight of our baby at birth, it would make it easier to predict some serious but rare complications. For example, birth trauma. Our estimates of the size of your baby can cause mom unnecessary stress and may lead to doctors intervening when it is not necessary.
As you near the end of your pregnancy, and wonder what your baby will weigh and how that could affect your labour and delivery process:
1. What is a “Big Baby”?
It’s difficult to pick a cut-off point. We usually consider babies weighing more than 4500 g (10 lb) as larger. As larger than normal. What we want to know is if your baby is too large for your pelvis.
Doctors consider weight when estimating a patient’s chances of having a successful vaginal birth. This is determined by three factors: “The passenger, the power, and the passage.”
We can only determine the “power” or force of contractions in utero once labour has begun.
The baby is the “passenger”. The baby’s weight is not the only thing that matters. It’s also important to consider the position of the child within the birth canal. The baby’s head direction can make a big difference in how quickly it descends into the birth canal.
The anatomy of the pelvis is called “passage”. What we are trying to determine when doctors perform vaginal examinations toward the end of pregnancy is how narrow the pelvis is. Can we reach the backbone? Can we reach the tailbone?
This is not an exact science, but it can be used to help determine the birth plan on the day of the delivery.
2. Ultrasound Does Not Provide a Reliable Estimate of Fetal Mass Shortly.
The ultrasound accuracy for a baby weighing 9 pounds is usually 15 to 20% off. This means that we could be over- or underestimated by more than one pound. Why are there so many variations?
The ultrasound uses volume to calculate the fetal mass. The ultrasound takes the measurements of the head circumference, some bones, and the waist circumference to estimate fetal weight. It can’t directly measure the density.
My patients understand it this way: I can use an ultrasound to measure the size of something. The structure will be the same, whether it is made from Styrofoam or stone. However, something made out of stone weighs much more than Styrofoam.
It is possible to calculate fetal body weight using standard measurements. However, not all babies will follow these rules. It is impossible to predict the exact weight of a newborn until it is born.
3. Who is at Risk of Having a Large Baby?
Mothers are at greater risk of having a large child if they have certain health or family history factors.
If your doctor has expressed concerns about the size and weight of your child, and you do not fall into one of these categories, I suggest having a candid conversation with them about their concerns and recommendations.
- Diabetes is a serious concern, particularly if the mother’s sugar level has not been well-controlled during pregnancy. The placenta can be affected by high glucose levels, which then affect the fetus. In response to high sugar levels in the mother, the fetus will produce insulin, which will stimulate its growth.
- Maternal overweight is a major risk factor. With rising obesity rates, we can expect to see more macrosomic children in the future.
- The history of a big baby. We would consider this trend of successive babies getting bigger and not smaller.
4. What are Some of the Concerns with Having a Large Child?
It is important to take into account the risks for both the patient, the mother and the child. The baby is at the greatest risk for birth trauma from fetal macrosomia, particularly if the baby has Shoulder Dystocia. This is when the baby’s body is not delivered easily after the head.
It’s a scary situation, but I understand why doctors recommend a C-section when they are worried about a large child. It’s a safer way to deliver the baby.
C-sections are associated with increased risk for the mother, as well as longer hospital stays, higher costs, and additional days in the hospital. These risks could be unnecessary since we often underestimate the fetal mass.
Plan That Works for You.
It can be difficult to determine which moms and babies are the most important. If doctors identify a woman’s baby as “large”, we can use interventions such as scheduled C-sections or labour inductions during labour. In the study that I mentioned, the average weight of babies predicted to be large was 7 pounds and 11 ounces. Not so big after all.
The American Congress of Obstetricians and Gynecologists has made clear recommendations. ACOG states that ultrasounds are no better at estimating fetal size than provider exams. Suspected macrosomia is not a reason to induce labour.
I suggest having an honest and open discussion with your physician about the information you have available. Talk about the size of your estimated baby, your obstetrical past, your physical examination, and any risk factors. When making a final decision, weigh the risks and benefits for both you and your child.
