Macrosomia is an obstetric condition that is associated with other potentially life-threatening complications to both the mother and the fetus.[1] The term macrosomia (big body) is derived from the Greek words “macro,” meaning big and “somia,” which refers to the body. The earliest use of the term was from the work of Robley Dunglison (1798-1859), an English physician and a medical writer. However, in modern medicine, according to the American College of Obstetrics and Gynecology (ACOG), two terms are applied to excessive fetal growth: “large for gestational age” (LGA) and “macrosomia.” Large for gestational age generally implies a birth weight equal to or more than the 90th percentile for a given gestational age. The term “macrosomia” implies growth beyond an absolute birth weight, historically 4,000 g or 4,500 g, regardless of the gestational age, although establishing a universally accepted definition for macrosomia is challenging.[2]
The etiology of fetal macrosomia can be categorized under two major classes:
Maternal Causes
Fetal Causes
The U.S. vital statistics report of the year 2015 indicates that seven percent of infants had a birth weight greater than 4000 grams, while one percent had a birth weight greater than 4500 grams. Other factors, such as age, race, genetics, ethnic groups are noted to also contribute to macrosomia. Hispanic pregnant women are observed to have a higher risk of fetal macrosomia compared to other races.
An interplay of physiologic and endocrine changes occurs in pregnancy, aiming at adequate nurturing of the developing fetus. The primary underlying pathophysiology of macrosomia could be broadly divided into maternal and fetal risk factors. However, maternal hyperglycemia appears to be the most significant factor in the pathogenesis of macrosomia. In the second trimester of pregnancy, an increase in the levels of the stress hormones such as cortisone, human placenta lactogen (HPL), and prolactin leads to the modest degrees of maternal insulin resistance, this, however, is countered by physiologic postprandial hyperinsulinemia. Patients with metabolic syndrome or other existing risk factors may be unable to mount an adequate hyperinsulinemic response leading to the development of hyperglycemia. Glucose transfer through the placenta occurs through facilitated diffusion that results in fetal hyperglycemia. This, in turn, brings about the hyperplasia of the beta islet cells of the fetal pancreas leading to overutilization of glucose by the fetus and hence an abnormal increase in fetal growth.
Findings from the Hyperglycemia and Adverse Pregnancy Outcomes study show a strong linear relationship between maternal glucose concentration and large for gestational age (LGA) fetuses, fetal adiposity, and fetal hyperinsulinemia.[5] A subsequent meta-analysis of the relationship between macrosomia (weight more than 4,000 g) and maternal glucose levels in women without diabetes demonstrates that a fasting blood glucose level or any abnormal value on oral glucose tolerance testing is associated with macrosomia. However, the fasting glucose level is more strongly associated with macrosomia. In women with gestational diabetes mellitus (GDM), the risk of macrosomia increases two-fold to three-fold, even with treatment. In a cohort of nearly 13,000 women, LGA newborns occurred in 29 percent of women with GDM type A1, 30 percent of women with GDM type A2, and 38 percent of women with preexisting diabetes.[2] N.B. Type A1 GDM: Patients typically have an abnormal glucose tolerance test but can keep blood glucose levels in the normal range with dietary changes alone. Type A2 GDM: Patients usually have an abnormal glucose tolerance test and abnormal glucose levels during fasting and after meals.
Pregnancy is a physiologic state that requires close monitoring and evaluation from the time of initial diagnosis to the expulsion of the full products of conception. Patients with high-risk pregnancies should be observed and monitored more closely.
History
A detailed history should be taken at the initial visit as well as in subsequent prenatal follow up visits. The obstetric provider should obtain a comprehensive history. The essential components of the medical history should include:
Physical Examination
A detailed physical examination should include monitoring of patient weight at each prenatal visit that should be correlated with suggested U.S. institute of medicine guidelines (IOM) as follows:
Any aberrations of the patient’s weight should prompt a repeat abdominal examination with measurement of fundal height correlated with the patient’s gestational age and the subsequent performance of Leopold maneuver by the obstetric provider. According to Tthe (ACOG) Ameican college of obstetrics and gynecology, weighting the newborn after delivery is the most accurate way to diagnose macrosomia, and no singular modality such as Leupold maneuver, fundal height measurement or an ultrasound scan can effectively diagnose macrosomia. A combination of these factors, on the other hand, should warrant a very high suspicion index.[2]
Maternal Evaluation
Maternal hyperglycemia has been a significant cause of fetal macrosomia and should be screened for by the following:
Gestational diabetes is confirmed when any two readings shown below are abnormal.
Fasting glucose greater than 95 mg/dL
Other maternal evaluations should include:
Fetal Evaluation
Macrosomic fetuses are at risk of various metabolic derangements and should be monitored closely. Laboratory measurements of the following electrolytes should be taken immediately after delivery.
Clinical evaluation of the neonate’s respiratory effort after birth is also essential as meconium aspiration due to fetal distress and transient tachypnea of the newborn (TTN) are common and tend to occur two to three times more frequently in macrocosmic babies especially if secondary to gestational diabetes.
The management of macrosomia is not clearly defined and should be multifaceted.
Medical Management
Induction of labor (IOL), which was widely recommended until recently, has been discouraged due to the lack of clear evidence on its significance in the management of macrosomia. Pregnancies complicated by fetal macrosomia in patients with pre-existing or gestational diabetes, and improved glycemic control via recommended pharmacologic and other interventions will lead to a reduction in the risk of perinatal complications. Pregnancies with macrosomia and no underlying diabetes pose a different challenge to the obstetric provider and other health care providers when appropriate treatment and intervention are needed. The American College of Obstetrics and Gynecology (ACOG) recommends an elective caesarian delivery to women with pregnancies complicated by macrosomia if the estimated fetal weight is above 5000 g and no underlying glucose intolerance or 4500 g with underlying glucose intolerance.[6] Assisted vaginal delivery, such as forceps or vacuum-assisted deliveries, should be performed with significant caution in women with macrosomic pregnancies.
Diet and Exercise Program
As previously stated, the two most important determinants of fetal macrosomia are uncontrolled maternal diabetes and excessive weight gain. The combination of a modified dietary regimen with adequate insulin therapy in pregnant women with diabetes might lead to a significant reduction in the likelihood of developing macrosomia. Graduated and tolerable exercise programs may decrease the risk of unnecessary weight gain during pregnancy and, in the long-term, reduce the risk of macrosomia if the patient has no other risk factors.[2]
The ACOG recommends against delivery before 39 0/7 weeks of gestation unless it is medically indicated. At this time, and until additional studies are reported, suspected macrosomia or LGA fetus is not an indication for induction of labor before 39 0/7 weeks of gestation because there is insufficient evidence that benefits of reducing shoulder dystocia risk would outweigh the harms of early delivery.[5]
A patient who delivers a macrosomic infant should be screened very carefully for previously undiagnosed diabetes. If such screening is negative, they should be monitored carefully in there following pregnancies. The goal of scheduled cesarean birth for suspected macrosomia is to reduce fetal morbidity or maternal morbidity, or both. Although fetal and maternal morbidity increase with birth weights more than 4,000 g, most births of macrosomic newborns are uncomplicated.[5]
Macrosomia and its complications and its risk factors can be subdivided under two broad categories:
Maternal Complications
Fetal Complications
Any female patient who gives birth to a newborn with macrosomia should be informed that her chance of having another pregnancy complicated by the same is increased to two to four-folds. Appropriate health education regarding excessive weight gain in pregnancy should also be emphasized to all expecting mothers during antenatal classes. It is currently recommended to screen patients with gestational diabetes during the postpartum phase for the development of prediabetes or type 2 diabetes mellitus. Women who develop gestational diabetes have three to seven times increased likelihood of developing type 2 diabetes mellitus within five to ten years after delivery.
The prediction of birth weight by ultrasonography or clinical measurement is imprecise. For suspected macrosomia, the accuracy of estimated fetal weight using ultrasound biometry is no better than that obtained via abdominal palpation. Women without contraindications should be encouraged to engage in aerobic and strength-conditioning exercises during pregnancy to reduce the risk of macrosomia. Control of maternal hyperglycemia reduces the risk of macrosomia. Therefore, maternal glucose optimization is recommended for pregnancies complicated by diabetes. Merely asking a parous woman for her estimate of the birth weight may provide an estimate as accurate as any other. In two studies, a parous woman’s ability to predict birth weight more than 4,000 g was as accurate as of that of clinicians using clinical palpation maneuvers alone.[2]
The management of fetal macrosomia could be somewhat challenging. The interprofessional team that consists of obstetric providers, pediatricians, neonatologists, endocrinologists, mental health practitioners, and registered dietitians plays a crucial role in caring for pregnant patients with macrosomia. The nurse should assist the obstetric provider in delivering the best standard of care for pregnant women during the preconception, antenatal, and postnatal periods. The nurse has a central role in educating pregnant women about the optimal control of their diabetes. The nurse should help the obstetric provider in the evaluation and monitoring of pregnant women with macrosomic babies. The nurse should keep a record of all maternal observations as well as clinical and ultrasound fetal weight estimations. Liaison between the members of the interprofessional team is essential to optimize maternal and fetal outcomes.
Registered dietitians should be included early on during the care of pregnant women with diabetes mellitus and women with a previous history of macrosomic infants. Educating pregnant women and their families about the risk factors and the maternal as well as fetal complications associated with macrosomia can not be overemphasized. Pregnant women with suspected fetal macrosomia should be encouraged to report any symptoms of reduced fetal movements to their providers. The nurse and diabetic educator should educate the women about the importance of the optimal control of their blood sugar, the importance of keeping logs of their blood sugar levels, and the attainment of proper weight gain during pregnancy. The members of the interprofessional team should support women and their families, and respect their views, concerns, and expectations about the timing as well as the mode of delivery at all times. The effective communication and harmonious coordination among the various members of the interprofessional team is the key to the successful management of pregnant women with suspected macrosomia.[Level 5]
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[2] | Macrosomia: ACOG Practice Bulletin Summary, Number 216. Obstetrics and gynecology. 2020 Jan; [PubMed PMID: 31856119] |
[3] | Catalano PM,Hauguel-De Mouzon S, Is it time to revisit the Pedersen hypothesis in the face of the obesity epidemic? American journal of obstetrics and gynecology. 2011 Jun; [PubMed PMID: 21288502] |
[4] | Nkwabong E,Nzalli Tangho GR, Risk Factors for Macrosomia. Journal of obstetrics and gynaecology of India. 2015 Jul; [PubMed PMID: 26243987] |
[5] | Macrosomia: ACOG Practice Bulletin, Number 216. Obstetrics and gynecology. 2020 Jan [PubMed PMID: 31856124] |
[6] | Practice Bulletin No. 173: Fetal Macrosomia. Obstetrics and gynecology. 2016 Nov; [PubMed PMID: 27776071] |
[7] | Said AS,Manji KP, Risk factors and outcomes of fetal macrosomia in a tertiary centre in Tanzania: a case-control study. BMC pregnancy and childbirth. 2016 Aug 24; [PubMed PMID: 27557930] |
[8] | Jolly MC,Sebire NJ,Harris JP,Regan L,Robinson S, Risk factors for macrosomia and its clinical consequences: a study of 350,311 pregnancies. European journal of obstetrics, gynecology, and reproductive biology. 2003 Nov 10; [PubMed PMID: 14557004] |
[9] | Menticoglou S, Shoulder dystocia: incidence, mechanisms, and management strategies. International journal of women's health. 2018; [PubMed PMID: 30519118] |