29 Weeks Pregnant - is my baby too big to be born vaginally?
Weekly pregnancy updates from a childbirth educator, doula and mum to 2 little girls. Come and join me on my journey as I share how I’m feeling, how baby is developing, what I’m doing to prepare, and some favourite resources!
When I had my morphology ultrasound around 21 weeks, the sonographer commented that baby was measuring in the 96th percentile, and that my provider would probably want to schedule growth scans during third trimester to make sure baby wasn't getting too big. I just smiled and thanked her, but I knew that we would not be planning any growth scans based purely on this comment...
Growth scans aren’t reliable
Firstly, growth scans are notoriously inaccurate. 50-60% of women who’ve had their labour induced early because the babies were expected to be “too big”, had babies who were average-size or small, with the estimate up to 15% different to the actual size... so not a reliable measurement at all! So many babies rushed into the world when they would have benefited from staying longer in utero. So many mums and babies subjected to medical intervention based on a scan measurement that is likely not spot on.
There are other ways of measuring growth
Secondly, I am blessed to have continuity of care with a midwife and she measures my fundal height every visit. If you have multiple people checking throughout your pregnancy there can be some discrepancy, but with the same one every time it’s generally a measurement which gives a good idea of what is going on with growth. From around 20 weeks, we’d typically expect the measurement in centimetres from the pubic bone to the top of the uterus to correspond roughly with the number of weeks pregnant you are, and grow at a rate of approximately 1cm per week. If there is a noticeable difference, either more or less, that could warrant further investigation, since there might be something unusual going on which is affecting the baby’s growth.
What does 96th percentile mean? Is it too big?
Thirdly, even if baby was measuring in the 96th percentile and continues to measure in the 96th percentile, what does that actually mean? It means that out of every 100 babies at the same gestation as mine, my baby is bigger than 95 and smaller than 4. But does that mean there is anything wrong? Absolutely not! Babies come in all shapes and sizes! And this doesn’t even take into account the fact that “due” dates can be off. What if the hospital is basing my dates off a likely date of conception 14 days from the beginning of my last menstrual cycle, but I didn’t actual ovulate/conceive until 20 days after? That leads to judging the size of a 22 week gestation baby according to the averages for 21 week babies! In my case I know the dates are spot on, but this can definitely happen!
Babies are designed the right size to be birthed by their mums!
Also, I’m probably also more chill about all this than I might otherwise be given my mother’s experience. I’m from a big family and my mother had natural births with most of us. Although she had a few babies under 3.5kg, the rest of us were bigger, including my 4.8kg brother! And my mum is only 155cm tall. So I’m used to the concept that babies are designed to be the right size to be birthed by their mums!
But sometimes they actually physically can’t be born vaginally…
A rare complication of pregnancy is known as cephalopelvic disproportion [cephalo=head]. In other words, the baby’s head and the mother’s pelvis are out of proportion, and the head physically cannot fit through. This can happen, but is extremely rare, and there is no way of knowing until labour if it will be an issue, since we just can’t accurately measure the head size of the baby before birth. This issue is about the baby’s head size compared to the mother’s pelvis size, rather than the baby’s overall size or weight as estimated from a scan. It’s also quite beside the point trying to get a measurement of the mother’s pelvis before birth, since the ligaments of the pelvis are designed to loosen and stretch during labour, facilitated by the mother having the freedom to move and be in upright positions.
Baby getting stuck in labour is usually treatable!
If baby gets stuck during labour, it’s much more commonly because they need to rotate into a position where their head will fit through the inlet of the pelvis more easily, or else because they have their head extended instead of tucking their chin. These are things that can typically be resolved through the use of Spinning Babies® techniques during labour.
Recommending induction for suspected big babies is common. Do your own research and make the best decision for you!
Despite all of this, it is extremely common for obstetricians to encourage induction at 38-39 weeks for suspected big babies. Do your own research if this happens to you, and decide whether based on your situation, the evidence, and your ob's recommendations, you think it is the right way forward for you or not. I’ve included links to a couple of useful articles in the resource section below.
What symptoms am I feeling?
I’m feeling fine, besides dealing with a bit of upper and mid-back pain if I don’t work on getting my core muscles engaging. My belly is getting big now and the muscles just want to let it goooo! 😂 I definitely need to focus a lot on core strength postpartum as well though. I didn’t experience this issue in my first pregnancy, but clearly haven’t got my core back to pre-baby strength and so the second and third times around I’ve been noticing it!
I have had a bit of acid reflux a couple of evenings, though nothing major. The weirdest time was one evening I’d snacked at 7pm, went to bed at 9 (plenty of time for the food to go down!)... and then woke up suddenly at 11pm with a moment of reflux! Seemed so strange, because if it was going to happen due to lying down I would have expected it much sooner!
How has baby been developing this week?
Roughly 39 cm and 1.4-1.6kg, baby’s eyelids are starting to open and they can make grasping movements with their hands.
What am I doing to prepare?
It’s been a routine week with my standard daily prep, which now involves
Spinning Babies recommended daily activities
breathing exercises
listening to positive birth affirmations (I do this while I exercise to save time and help my focus!)
listening to a KG Hypnobirthing relaxation and birth visualisation audio (though I don’t get to this every day)
drinking red raspberry leaf tea
eating dates (the studies most people refer to started from a use of dates at 36/37 weeks, but I have always started sooner - I like them and they help my energy!)
I haven’t had any pregnancy visits or appointments this week, though I will go out today for blood and urine testing as we aim to rule out any pathological causes for my low platelets and low ferritin diagnosis I talked about last week.
Resources:
Dr Sara Wickham, Induction for big baby: what’s the evidence?
Spinning Babies, Is My Baby Too Big?
And that’s it for this week! 🌿💛
[Image credit: Photo by hessam nabavi on Unsplash]