I wanted to link you to the current Lamaze research summaries
(June 2008) by Amy Romano, but I'm getting an error message at the
moment, so I went to my old e-mails and did a copy-and-paste of her
summary of a study on the effect of fetal weight estimates.
Prenatal Diagnosis of Suspected Fetal Macrosomia Increases
Risks of Cesarean Section and Maternal Morbidity without Improving
Sadeh-Mestechkin, D., Walfisch, A., Shachar, R., Shoham-Vardi,
I., Vardi, H., & Hallak, M. (2008). Suspected macrosomia?
Better not tell. Archives of Gynecology and Obstetrics,
doi: 10.1007/s00404-008-0566-y. [Abstract]
Summary: In this prospective observational
trial, researchers followed 145 women thought to be carrying babies
weighing more than 4000g (about 8lb, 13oz) to evaluate the
reliability of sonographic and clinical estimates of fetal weight
and to determine whether a diagnosis of "suspected macrosomia"
affects pregnancy management or outcomes. To answer these
questions, they first divided the "suspected macrosomia" into two
subgroups depending on whether the babies in fact weighed more or
less than 4000g. This resulted in a "false-positive" subgroup of 82
babies thought to be macrosomic but actually weighing less than
4000g and a "true-positive" group of 63 babies thought to be
macrosomic and indeed weighing more than 4000g.
The researchers compared outcomes between these two groups, then
compared the "true-positive" group to all other births of
macrosomic infants to women admitted to the same hospital in the
study period (i.e., women giving birth to infants weighing over
4000g but who did not have a prenatal diagnosis of suspected
The study confirms an existing body of literature that tells us
that prenatal methods for detecting macrosomia are not
reliable—only 44% of babies suspected to weigh over 4000g
actually did. Clinical estimates (those performed by a care
provider using palpation) were more reliable than ultrasound
estimates, but were still off by more than 10% in one out of every
The 145 women with suspected macrosomia were assigned by the
admitting doctor to elective cesarean surgery (16%) induction of
labor (39%) or observation awaiting labor (46%). Thirty-five of the
56 women who underwent induction and 47 of the 66 women who were
admitted in spontaneous labor gave birth vaginally, for an overall
vaginal birth rate of 57% (including 2% who had instrumental
vaginal births). The remaining women gave birth by cesarean surgery
either before (21%) or during (22%) labor.
When researchers compared outcomes of the "true-positives" with
the "false-positives" within the "suspected macrosomia" group,
there were no differences in maternal or infant complications.
When the researchers compared the true-positive macrosomic
infants in the study group (those suspected to weigh and actually
weighing >4000g) to the macrosomic infants in the comparison
group (those not suspected to be macrosomic prior to birth), they
found much higher rates of intervention and related morbidity in
the study group. The cesarean surgery rate for macrosomic infants
in the suspected macrosomia group was 57%, compared with only 17%
for macrosomic infants in the comparison group (absolute difference
40%). Likewise, 25% of macrosomic infants in the study group were
induced compared with 14% in the comparison group (absolute
difference = 11%). There was no difference in shoulder dystocia
between the two groups. However, maternal morbidity (including
hemorrhage, wound infection, wound dehiscence, fever, and use of
antibiotics) was significantly higher in study group, most likely
because of the much higher rate of cesarean surgery in this
Significance for Normal Birth: The
concern that a baby is growing "too big" is one of the most common
reasons cited for induction of labor and also prompts decisions to
perform cesarean surgery both before and during labor (Declercq,
Sakala, Corry, & Applebaum, 2006). However, there is strong and
consistent evidence that elective induction or cesarean surgery for
"suspected macrosomia" does not improve outcomes and expert bodies
including the American College of Obstetricians and Gynecologists
oppose routinely interfering when a baby is suspected to be large
(American College of Obstetricians & Gynecologists, 2004).
This study, summed up by its title, "Suspected macrosomia?
Better not tell" provides damning evidence that shows clearly that
the provider's belief that the baby is "too big" is itself a strong
risk factor for injudicious intervention and poor health
An initial suspicion that the baby is large may instill fear in
the pregnant woman which may impede both her confidence in her body
and her labor progress. Slow labor progress reinforces the
suspicion that the baby is big and more aggressive management
ensues. This management often hinders the woman's ability to move
freely and assume the positions that may help her baby negotiate
through her pelvis, further slowing progress and reinforcing the
perceived need for surgical intervention. Based on this study and
previous evidence, women should strongly consider refusing tests
late in pregnancy intended to estimate fetal weight.
The estimate itself may be bad for her health because the care
provider's expectation that the baby will be macrosomic appears to
increase both unnecessary medical intervention and the morbidity
that may accompany it.
American College of Obstetricians and Gynecologists. (2004).
Ultrasonography in pregnancy. ACOG Practice Bulletin No. 58.
Obstetrics and Gynecology, 104, 1449–58.
Declercq, E., Sakala, C., Corry, M. P., & Applebaum, S.
(2006). Listening to mothers II: Report of the second national U.S.
Survey of women's childbearing experiences. New York: Childbirth
As for amniotic fluid volume estimates, here is a study that, as
I recall, was summarized in last year's Lamaze research summaries,
but since I can't get at those, I give you the citation and the
Manzanares S, Carrillo MP, Gonzalez-Peran E, et al. Isolated
oligohydramnios [low amniotic fluid volume] in term pregnancy as an
indication for induction of labor. J Matern Fetal Neonatal Med
OBJECTIVE: To evaluate the outcome of active induction of labor
for isolated oligohydramnios in low-risk term gestation. METHODS:
This retrospective study analyzed the obstetric and perinatal
outcome of 412 singleton term pregnancies with cephalic
presentation and no maternal risk factors or fetal abnormalities.
Two groups were compared: 206 deliveries after induced labor for
isolated oligohydramnios, and 206 deliveries matched for
gestational age following spontaneous labor with normal amniotic
fluid index. RESULTS: The overall rate of cesarean deliveries and
cesarean deliveries for nonreassuring fetal status, and operative
vaginal delivery rates and those for nonreassuring fetal status
were higher in the oligohydramnios group than in the control group.
There were no differences between groups in neonatal outcome or
perinatal morbidity or mortality. CONCLUSION: Active induction of
labor in term low risk gestations with isolated oligohydramnios
translated into higher labor induction, operative vaginal delivery
and cesarean section rates. This led to increased maternal risk and
an increase in costs with no differences in neonatal outcome.
Unfortunately, though, since conventional obstetric prenatal
care consists of instilling fear from the very first visit, by the
end of the pregnancy, most pregnant women are probably not