Macrosomia and Vaginal Birth

One word a pregnant mother does not want to hear with regard to her baby is "macrosomia". In many obstetric practices across America, this term is a death knell for a woman's desire to give birth naturally. If she isn't automatically scheduled for an early induction or a c-section, she knows that the diagnosis means she's on the "high risk" list and that her caregivers will be even quicker than normal to tell her that her birth is not progressing well.

What is macrosomia?

Fetal macrosomia is defined in two different ways. The commonly accepted numbers in medicine today are 4000-4500 g (8 lb 13 oz to 9 lb 15 oz). A baby may also be macrosomic if it is larger than 90% of other babies of it's gestational age (taking sex and ethnicity into account). Somewhere between 1% and 10% of pregnancies are affected by macrosomia based on these numbers.¹ One important (and sometimes frustrating fact) is that a true and accurate diagnosis of macrosomia can only be made after the baby is born. Sonography can give an estimate of fetal size, but can be off by as much as 2 lb. I can attest to this potential for inaccurate diagnosis of macrosomia with my own experience. When I was 39 weeks pregnant with my first child, I was told that my baby was already 8 pounds and that if I didn't have an induction soon, I'd be at risk for serious complications. A few days later I delivered my son (without an induction), and he weighed in at 6 lb 14 oz.

How big is too big?

I have also experienced the opposite side of this coin. With my second and third sons, sonography accurately predicted large babies. They were born at 9 lb 15 oz and 10 lb 8 oz, respectively. Therein lay another problem. Although I had supportive midwives, the doctors they worked with, for lack of a better term, "freaked out". The weeks preceding those births were much more stressful and unpleasant than the actual labors. The primary concern with macrosomia is that shoulder dystocia will complicate the deliver. This complication is rare overall, and occurs unpredictably with babies of all sizes, but the risk does rise with macrosomia.²

Although it is a concern, the risk is still small. And though you wouldn't know it from the medical model of childbirth, there are techniques that are very effective in unsticking those "sticky" shoulders a good portion of the time. Ina May Gaskin and the midwives at The Farm have been practicing these methods with great success for years. Along with these techniques, the simple change of position from lithotomy (on the back, with legs in stirrups) to the hands and knees position makes a large difference in the pelvic outlet and may be all that's needed to allow a large or wide-shouldered baby to pass through with little or no complication in many cases.³ In my case, this hands and knees position allowed easy delivery of my two very large sons, and I also found it to be the best position for me, for coping with the intensity of transition contractions. I was very grateful at the time that my midwives were aware of the benefits of this position and did not insist on practices that would have kept me on my back and put myself and the babies at higher risk.

Not being able to properly diagnose macrosomia until after a baby's delivery makes impossible to say which baby will be delivered with ease and which will need some help. As with almost anything else related to birth, there are risks either way, and each woman and her baby need to be treated as individuals, and have the particulars of their circumstances carefully weighed in the balance of risks versus benefits. And every once in a while, there will be a baby born who beats all the odds, like baby Johnathan born in Massachusetts this year. He was born vaginally, with no complications, and weighed in at 13 lb. 2 oz.⁴ Clearly he was not "too big" for his normally-sized mother, and it does make one wonder why an 8-pound baby has in recent years become "much too big" for most women, necessitating early inductions or cesarean sections.

¹Macrosomia, Allahyar Jazayeri MD, PhD, eMedicine Obstetrics and Gynecology
²Practice Guildelines: ACOG Issues Guidelines on Fetal Macrosomia, Joanne Chatfield, AAFP
³A New (Old) Maneuver for the Management of Shoulder Dystocia, Meenan, Gaskin, Hunt &Ball, The Farm
⁴Mom gives birth to 13 lb 2 oz baby in Methuen, staff, WDHD/NBC