Ask an OB: "You can't grow a baby too big . . ."

"Ask an OB" is a weekly series with Dr. Maude "Molly" Gurein, MC, FACOG.  If you have a question you'd like to ask her, please share it with us here. 

What do you think of the statement, "You can't grow a baby too big for your body to birth."  Can you also talk about the importance of Gestational Diabetes screening?  What danger is there in skipping that test?  Is there a weight gain at which a pregnant woman would be suspected for Gestational Diabetes?  For example if she has gained 60-90lbs and is craving sugar toward the end of her pregnancy, would that be a warning sign? - Lansing Mom

“You can’t grow a baby too big for your body to birth” is a completely false statement.  The latest worldwide statistics on maternal mortality show that 8% of pregnancy related deaths in women are due to “obstructed labor” – in other words, baby actually WAS too big and mom DIED trying to deliver it. So let’s not spend any time debating the validity of this statement – it’s nuts.
 
The thing I really hate about this statement is that it implies that if you have a C section for this reason, you just didn’t try hard enough. If only you had been stronger, tougher, more deserving – a better person – you would have been able to do it. You’re a quitter, a wimp, a weakling, not deserving of respect. And the opposite is familiar as well isn’t it? Somehow those lucky women who blast 10 pound babies out in 3 hours with 1 push are proud and self-satisfied, revered and rarified. Let’s just accept the fact that some women have big pelvises and others don’t, and that babies vary in size and shape. Usually mother nature puts the right sized baby in the pelvis – 90% of the time babies fit in moms over 5’1” tall. In moms under 5’1” 80% of babies fit! Make sure your contractions are strong enough and be patient – if your pelvis is big enough the baby will come. If not, you will have a well deserved and life saving cesarean section – personally, I think you deserve MORE credit for that delivery than the 3 hour, 1 push delivery!

Diabetes is related to this question of bigger babies. Gestational diabetes mellitus is increasing in frequency, mostly due to increasing obesity rates in moms, now occurring in about 7% of all pregnancies. Even in moms of normal weight, GDM is present about 5% of the time. So the chances are small that you will be affected – 95% of the time you will be fine. Why do we care in that case? Well, we care because if you do have uncontrolled GDM it can greatly increase the chance for complications in you or in your baby.  Look at this data from a 1998 study of about 800 women, which remained significant after controlling for maternal age, race, parity, body mass index, pregnancy weight gain, and gestational age at delivery.
 

	Uncontrolled GDM	Controlled GDM	No GDM
Baby over 8.5#	44%	9%	5%
Shoulder dystocia	19%	3%	3%
Birth trauma	25%	0.3%	0%

(Am J Obstet Gynecol 1998;178:1321-32)

Note that you won’t give yourself diabetes by gaining too much weight, but that pre-pregnancy obesity IS related to developing GDM. “Sugar craving” is unrelated to GDM as far as I can tell. Bottom line: even though your risk of having GDM is small, if you do have it and don’t control it, the chance for problems is quite high. In the interest of as many vaginal deliveries as possible, let’s control GDM so we can reduce babies that are too big to fit out vaginally and safely.

You can read more about Dr. Maude "Molly" Guerin, MD, FACOG, right here.