Ultrasound is widely believed to be the most accurate method of estimation of foetal weight. Yet in 1988, Miller, Brown, Khawli, Pastorek & Gabert in “Ultrasonographic identification of the macrosomic fetus” found that the typical mean error ranges from 300 to 550g (11.6 to 19.4 oz). That’s around a WHOLE POUND! In 1992 Chauhan, Lutton, Bailey, Guerrieri & Morrison In “Intrapartum clinical, sonographic, and parous patients‘ estimates of newborn birth weight” found that ultrasound was the least accurate of the three methods, i.e: it was less accurate than the educated guess of the obstetrician or mother! In their study “Pregnancy outcome following ultrasound diagnosis of macrosomia” Delpapa & Mueller-Heubach found that “In 66 of 86 women (77%) delivering within 3 days of ultrasound examination, estimated fetal weight exceeded birth weight. In only 41 of these 86 women (48%) were the estimated fetal weights within the corresponding 500-g category of birth weight” – That’s quite some difference!
- Multiparity (not your first baby)
- Birthing a previous macrosomic baby
- A prolonged period of gestation
- Carrying a male baby
- Parental Stature
- Excessive weight gain during pregnancy
If a woman enters labour free from fear and anxiety oxytocin (the hormone of labour) will be free to flow, her uterus will contract efficiently, endorphins (natural morphone like pain relievers released during labour) will flood her body, adrenaline will be kept to a minimum ensuring that her uterus is well oxygenated and making her as comfortable as possible. She will move instinctively into positions which freely open her pelvis, such as a squatting position (where the pelvis is said to have up to 30% more capacity) or perhaps on all fours – both superb positions for birthing a big baby.
The size of a baby then in a normal, physiological birth – where anxiety and “big baby” talk is not present – is largely irrelevant, it doesn’t make it more painful and it doesn’t make it harder! The following article, by midwife Gloria Lemay, is a MUST read for anybody worrying about birthing a large baby and wondering whether their pelvis is “big enough” Pelvises I have known and loved.
So, Is an Induction of Elective C-Section Not Necessary for a Suspected Big Baby Then?
You may have been advised that it would be best for you and your baby if you are induced early? or perhaps an elective C-Section has been advised. You might have been told that you baby is much more likely to get stuck (also known as “shoulder dystocia”), but does the research agree?
Actually the vast majority of research into Macrosomic babies indicates that elective C-Section and induction for just a suspected large baby is a bad idea, deeming it unneccessary, needlessly expensive and not effective at preventing birth trauma to the mother or baby. When looking at induction the research is in fact even more scathing, with many suggesting that early inductions only serve to raise caesarean section rates without altering outcomes for the mums or babies.
Finally, just suspecting a macrosomic baby can lead to problems, with one study indicating that the risk of cesarean section was substantially higher (52 versus 30 percent) in pregnancies in which macrosomia was suspected, even after controlling for birth weight and other confounding variables. More importantly, the difference in the cesarean section rate was attributable to a greater proportion of failed inductions for the macrosomia in the group in which it was suspected.
Lets take a quick whistle stop tour of clinical research into suspected foetal macrosomia and birth outcome. Lets start with my favourite, a Cochrane Review looking at “Induction of labour for suspected macrosomia”, April 1998 suggested that elective C-Sections and inductions for a suspected big baby was a bad idea. The summary of the review is as follows. Important points have been highlighted:
“Babies who are very large (macrosomic – over 4500 g) can sometimes have difficult and, occasionally, traumatic births. One suggestion to try to reduce this trauma and to reduce operative births has been to induce labour before the baby grows too big. However, the estimation of the baby’s weight in utero is difficult and not very accurate. Clinical estimations are based on feeling the uterus and measuring the height of the fundus of the uterus, and both are subject to considerable variation. Ultrasound scanning is also not accurate. Induction, if undertaken too early, can lead to babies being born prematurely and with immature organs. The review of trials, assessing induction of women when it was suspected that their baby was above 4 kg, found three trials involving 372 women, none of them with diabetes. There was no evidence of any benefit in terms of caesarean section or instrumental births, or in outcomes for the baby. However, these studies were too small to be sure of the outcomes. Further research is in progress.”
The results section of the Cochrane Review also states: “Perinatal morbidity was not statistically different between groups (shoulder dystocia).”
In the Archives of Gynecology & Obstetrics, September 2008. Sadeh-Mestechkin, Walfisch, Shachar, Shoham-Vardi, Vardi & Hallak, in their study entitled “Suspected macrosomia? Better not tell” noted that: “Our ability to predict macrosomia is poor. Our management policy of suspected macrosomic pregnancies raises induction of labor and cesarean delivery rates without improving maternal or fetal outcome.”
In 1994, in The Chinese Medical Journal, Yan, Chang & Yin, in their article “Elective cesarean section for macrosomia?” studying the births of 207 macrosomic babies concluded that: “Elective Cesarean section on macrosomic infants to prevent dystocia is not recommended because most of them can be delivered vaginally.”
In 2000, in the European Journal of Obstetrics, Gynecology & Reproductive Biology, Mocanu, Greene, Byrne & Turner studied the births of 828 macrosomic babies born over a 5yr period in their report entitled “Obstetric and neonatal outcome of babies weighing more than 4.5 kg: an analysis by parity” they concluded that: “The poor antenatal predictability of macrosomia, the high rate of vaginal delivery and the low incidence of shoulder dystocia would not support the use of elective caesarean section for delivery of the macrosomic infant either in primigravidae * or multigravidae.”
* Editor’s Note: Primigravidae = First Time Mother, Multigravidae = Second or More time mother.
In april 1995 in Obstetric Gynecology in their research “The outcome of macrosomic infants weighing at least 4500 grams: Los Angeles County + University of Southern California experience” looking at 227 births of macrosomic babies, Lipscomb, Gregory & Shaw noted that: “Vaginal delivery is a reasonable alternative to elective cesarean for infants with estimated birth weights of at least 4500 g, and a trial of labor can be offered.”.
In 2006 in the American Journal of Obstetrics & Gynecology, Chauhan, Grobman, Gherman, Chauhan, Chang, Magann and Hendrix reviewed the evidence for performing an elective ceasarean or an induction for suspected macrosomia, in their article”Suspicion and treatment of the macrosomic fetus: a review.” they noted that: “Due to the inaccuracies, among uncomplicated pregnancies suspicion of macrosomia is not an indication for induction or for primary cesarean delivery.”
In 1996, Rouse, Owen, Goldenberg, Cliver, in “The effectiveness and costs of elective cesarean delivery for fetal macrosomia diagnosed by ultrasound” published in JAMA 1996. estimated that “to prevent one case of permanent brachial plexus injury, 3,700 women with an estimated fetal weight of 4,500 g would need to have an elective cesarean section for suspected macrosomia at a cost of $8.7 million per case prevented.“
Hmmm – perhaps that early induction isn’t looking like such a good idea after all? What are your birth options then? READ ON – to see part two – Birthing a Big Baby.