Macrosomia: What Causes Big Babies In Pregnancy?

According to statistics, 10% of babies experience macrosomia. This medical condition may involve risks at birth. The bigger is the baby, the bigger are the risks involving the birth.


What Is Macrosomia?

The normal weight of a newborn is of up to 4 kg. Anything over this limit involves a macrosomic baby, which means a fetus with a weight over the normal limit.

As most statistics show, 10% of babies are macrosomic. Although they have a weight higher than the normal limit, this doesn`t mean their life is influenced in a negative way.

How Do You Know If the Newborn Will Be Macrosomic?

The first clue is represented by the mother`s tummy. If this is too large in relation with the gestational age of pregnancy, then the doctor might assume that the fetus is macrosomic. However, before pregnancy is very hard to if and how big will the baby be, even by ultrasound. After birth and when the baby is weighed, the doctor can pronounce himself.


The determinant causes for this medical condition split in primary and secondary. Among the primary causes are large vessels, Wiedemann-Beckwith syndrome, Sotos syndrome. All these pathologies present as common symptoms the excessive intrauterine growth associated with different abnormalities.

Among the secondary causes with an essential role is played by glucose metabolism abnormalities, mainly gestational diabetes or maternal insulin-dependent diabetes. Women with diabetes present during the last trimester of pregnancy hyperglycemia. A percentage of 75% from the concentration of mother`s glucose will pass to the fetus, crossing the placenta through a process known as facilitated diffusion process. Therefore, the baby becomes hyperinsulinemic, because of the increased insulin secretion and excessively anabolic. Glycogen surplus accumulates in the liver, and triglycerides will deposit in the adipose cells, therefore leading to the increase of the subcutaneous fat. – More info!

Another factor for macrosomia is determined by the difficulties of homeostatsis difficulties.

The rhythm of baby growth doesn`t determine a simultaneous acceleration of his maturation. Although they seem gigantic at first sight, they are less mature than you would expect.

The poor metabolic state will prevent them to adapt to the extrauterine life as other babies born at term. Macrosomic children will encounter difficulties regarding their resistance to the transient hypocaloric regimen that follows the umbilical cord`s clamping, because hyperinsulinism decreases glycemia.

The children of diabetic mothers present an increased risk of polycysticemia, idiopathic respiratory distress, hypocalcaemia, renal vein thrombosis.

Macrosomia can also be caused by the increased extracellular volume, secondary to placental growth in case of placental corioanginoma or fetoplacentar anemia.

The excess weight of the mothers is another important factor of this medical condition. Mothers with extra weight give birth to children with a greater weight than 4.000 g.

Risk Factors

Most of the times, the only cause for macrosomia is the genetic factor.

If we are talking about the factors which can be controlled, the most important of these is the future mother`s increased levels of blood sugar. The high blood sugar may caused by gestational diabetes.

However, macrosomic children can have obese mothers as well, especially if they gain weight during pregnancy. – Read this!

An important aspect is also the baby`s gender, as boys have a larger weight than girls.

Mothers who already gave birth to a macrosomic child have higher chances to repeat to have another macrosomic child in a future pregnancy.

Still, mothers who show these risk factors don`t need to concern themselves. It`s possible for the newborn to have a normal weight, just as a mother who doesn`t show any risk factors can have a macrosomic child.

The high variations of weight at birth couldn`t be explained by experts yet.

Possible Complications

As already mentioned, macrosomia can lead to a lot of birth issues. The bigger is the fetus, the higher are the risks for the birth to be more difficult.

The mother may experience coccyx wounds, perineal injuries or haemorrhage. Also, there`s also the risk of shoulder distress, which means that the fetus may remain with his shoulder stuck behind the mother`s pubic bone and unable to move forward. This is a very serious and rare birth complication which requires immediate resolution, so the baby won`t be affected severely.

Macrosomia also means more chances for Caesarean birth. Although is hard to establish the fetus`s weight before birth, the doctor may decide if he performs C-section to a mother with a large belly only to avoid complication.

If the birth is complicated, the newborn`s problems will be related to those respective complications. Shoulder distress may lead to a clavicle fracture, which eventually may heal with any issues. Otherwise, macrosomia isn`t associated with severe health issues. – Click here!

Bigger problems may have the mother if she gives birth naturally. Depending on the wounds he experienced in her perineum, restoration might take more or less time. However, the mothers who follow the advice of a specialist doctor shouldn`t find any long-term issues.


The diagnosis is placed based on the paraclinic investigations (pelvic ultrasound) and history.


The treatment for this medical condition doesn`t present any symptoms. Depending on each personal case, surgery for treating various fractures, or oxygen therapy for perinatal asphyxia.

Image courtesy of emaxhealth.com

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