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Obesity & Pregnancy Outcomes

Body shaming has garnished a great deal of attention lately and I am loving every moment of it. Whether I am teaching yoga or extending primary care services, supporting women in loving and accepting themselves as they are is a huge priority of mine, but this is separate from also being authentic and addressing how we might work together to optimize their health. Obese women are at increased risk for multiple labor abnormalities, including postdate pregnancy, failed induction of labor, prolonged labor, cesarean delivery, and postpartum hemorrhage. While midwives can be very empathetic and often feel a need to advocate and protect larger women from the onslaught of medical interventions and the consequences of this care, we also toss back and forth the wisdom in extending care to especially obese women in a birthing environment outside the hospital.


One-third of reproductive-aged women are now classified as obese so understanding these risks is paramount for optimal outcomes. Really understanding these risks is challenging though, because most of these women are also undergoing inductions or scheduled cesarean births. The literature seems to suggest however, that obese women are less likely to enter spontaneous labor at term and are more likely to progress towards post-dates. This is especially unfortunate since obese women already face higher rates of stillbirth.


The larger a woman, the more likely she is to undergo a cesarean section for reasons generally related to failure to progress and cephalopelvic disproportion, which is why midwives often feel inclined to care for these women in the home or birth center setting, as we are more supportive of the extremes of labor when accompanied by reassuring fetal and maternal status.


Wound infections are also increased in this population, as well as longer operative times, excessive blood loss, postoperative endometritis, among other complications. Reducing cesarean sections among obese women is a huge priority for optimizing outcomes of both women and their infants. Consider as well, that these women often go on to have subsequent surgical births with welcome further morbidity. When they do opt for a vaginal birth after prior cesarean, obese women are more likely to suffer uterine rupture or dehiscence.


Calculators have been developed to assist women in understanding their chance of success for vaginal birth based on the body mass index. The National Institute of Health MFMU Network has created such a calculator, which weighs the risks of a trial of labor against a repeat cesarean.


Women who are obese have higher rates of emergency cesarean sections due to nonreassuring fetal status, which isn't well understood, but may be related to placenta pathology. They seem to have higher rates of inflammatory infiltrates and maternal vasculopathy. They should be made aware as well, that due to more abdominal adiposity, monitoring of the fetus can be especially challenging. Some practitioners will routinely rupture the amniotic sac so they can place internal monitors, which invites risk themselves, but of course this must be weighed against the need to evaluate fetal status.


Cesarean sections which are emergent can take longer than would be necessary for a women of a lower body mass index, and this is exaggerated even more so with repeat cesarean sections. Anesthesia is a significant risk when obese, as they can struggle to obtain and maintain proper placement whether regional or general. Obese women suffer more sleep apnea. More often these women have other medical conditions, such as hypertension or gestational diabetes. Obtaining an anesthesia consult during the prenatal period may be advantageous, or being open to placing a walking epidural in early labor so in the event an emergency cesarean is required, placement for anesthesia has already been established.


Slower Progression in Labor


The contributing factor for why women who are obese tend to progress slower in labor is somewhat a mystery, but the leading theories are fat deposits in the pelvis, decreased maternal expulsive efforts (less muscle strength and coordination or fitness ability to push effectively), and impaired uterine contractility. Limited data suggests that the myometrial contractility may be impaired in obese women, and one study found that myometrial strips from obese women contract with less frequency and amplitude that those from normal weight women. Interestingly, low density lipids have shown to inhibit the contractility of myometrial strips; however, measuring maternal cholesterol does not seem to correlate with childbirth outcomes.


Research has also shown us that oxytocin augmentation is less successful in obese women and higher doses is required, so that practitioners now theorize that oxytocin may not be as effective in obese women. Interestingly, there is thought that myometrial oxytocin receptor genes and protein expressions are affected by maternal obesity, although this did not seem to present in in vitro samples. Another potential possibility is that because more obese women are augmented in early labor because they inherently have longer first stages of labor, that this may not be about their body's response to labor, but instead when this is initiated and their overall longer duration of labor. Interestingly, this abnormal labor progression among obese women seems to be isolated to the first stage of labor. It seems obese women have similar second phase labors as those of normal weight; therefore, management does not need to be altered for obese women.


Midwives are experts in labor management and are likely the most ideal attendant, with the patience and labor enhancement know-how, to support women who are obese through what may be a longer labor, minimizing their incidence of cesarean section and overall reducing their risk of morbidity. However, this is prefaced with the opinion that midwives should be exceedingly diligent about identifying abnormalities in blood sugars in obese women, to assure the fetus is maturing healthy in both tone and size. Additionally, close monitoring of blood pressure is important for optimizing placenta development, as well as optimal fetal status.


Homebirth & Obesity


One of the greatest concerns about obese women in the homebirth setting, potentially even the birth center setting, is how a transfer might be managed. Are paramedics capable of transferring these women utilizing their equipment, navigating the rooms and passageways of the client's home and driveway, especially the restroom facilities where many women find comfort in labor. If a women with a large body mass index labors in the pool, and suffers an obstetrical emergency, can she be readily removed to assist in an impacted shoulder or hemorrhage scenario? What are the standards among other midwives in your area regarding obesity, and even the midwives at the local hospitals?


There is much to consider with regards to the challenges that face the pregnancies and childbirth experiences of women who are obese, but there seems clear benefits and risks to each birthing environment, and a collaboration between midwife and obstetrician seems optimal, no matter which environment is ultimately chosen.

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