Pregnancy

Fetal growth and intrauterine growth restriction (IUGR)

When do we talk about growth disorders or intrauterine growth restriction (IUGR) during pregnancy?

When evaluating fetal growth in pregnancy, 3 considerations must be made:

  • growth must be related to gestational age to verify that gestational age has not been incorrectly determined
  • If the gestational age is correct, the ultrasound evaluates the dimensions indirectly
  • While accepting the limits listed above, the measures must be compared with “normal” values based on a reference population.

Differences from “normality” may be due to factors inherited from parents such as race and height.

It is important to examine all these aspects in order to identify the real cause of a growth disorder.

Depending on the cause, in fact, the complications that derive from it can vary greatly. If it is due to utero-placental insufficiency, important complications may arise including, unfortunately, perinatal death or intrauterine death.

Intrauterine growth restriction or small by constitution?

All fetal growth abnormalities are defined as the inability of a fetus to grow according to its genetic potential.

However, this potential is not known and therefore the assessment of growth is based on the expected size by gestational age detected with ultrasounds.

Three percentile thresholds are used:

  • less than 3° orcentile
  • below the 5th percentile
  • below the 10th percentile

Estimated weight below the 10th percentile means that it is lower than that of 90% of babies of the same gestational age.

Fetuses with an estimated weight below the 10th percentile are defined as small for their gestational age (SGA). Not all EMGs have a pathological restriction of growth.

It is therefore essential to distinguish  between fetuses that are small but healthy (that is, they are small by constitution) and those that have reduced growth due to a pathology.

Causes of intrauterine growth restriction IUGR)

One of the most frequent causes is related to the activity of the placenta. The placenta is a fundamental element for fetal growth, since it provides all the substances necessary for growth and is responsible for gas exchanges between mother and baby.

Other causes may be related to the state of health of the mother such as

  • Advanced diabetes
  • High blood pressure or heart disease
  • Infections such as rubella, cytomegalovirus, toxoplasmosis and syphilis
  • Kidney or lung disease
  • Malnutrition or anemia
  • Sickle cell anemia
  • Smoking, alcohol or drug abuse

Other possible fetal causes include chromosomal defects in the baby or multiple pregnancy.

How is fetal growth restriction diagnosed?

In clinical practice through the symphysis-fundus length and, above all, with ultrasound measurements.

Growth disorders are rare before 24 weeks of pregnancy and growth assessment is typically done after 24 weeks of pregnancy.

The symphysium-bottom length

It is a measure that is made from 24 weeks of gestation It measures the distance between the woman’s pubic symphysis and the uterine fundus.

The symphysis-bottom distance after 24 serttimane must be equal to the week of gestation ± 2 cm up to 36 weeks. Between 36 and 42 weeks the distance must be equal to the week of gestation ± 3 cm.

This procedure has margins of error related to the method itself and to the operator. Two major studies have suggested that a measure of reduced symphysis and bottom length identifies only 24-50% of fetuses with birth weight below the 10th centile.

Ultrasound

It remains the most sensitive method for studying fetal growth. Several successive measures are needed to identify an abnormality of fetal growth, especially of abdominal circumference. But biparietal diameter, head circumference and femur length are also evaluated.

Subsequent measurements are compared with specific ultrasound growth charts that take into account maternal and fetal characteristics, so as to be able to distinguish between small fetuses, but which have normal growth, from those in which the growth was initially in the normal range but which later fell are a certain centile.

Fetal arterial and venous Doppler

Doppler flow is a technique that uses sound waves to measure the amount and speed of blood flow through blood vessels. Doctors can use this test to check blood flow in the umbilical cord and vessels in the baby’s brain.

Cardiotocography

This test involves inserting sensitive electrodes into the mother’s abdomen. The electrodes are held in place by a light elastic band and connected to a monitor. Sensors measure your baby’s heart rate and display them on a monitor or print them.

Weight checks

Doctors regularly check and record the mother’s weight at each prenatal check-up. If a mother is not gaining weight, it could indicate a growth problem in her baby.

Amniocentesis.

Amniotic fluid tests taken with amniocentesis can detect infections or chromosomal abnormalities that could cause fetal growth restriction.

Can it be prevented?

Fetal growth restriction, IUGR, can occur even when a mother is perfectly healthy. But there are some things mothers can do to reduce the risk of IUGR and increase the chances of a healthy pregnancy and baby.

  • Perform all scheduled prenatal checkups: detecting potential problems early allows them to be treated earlier.
  • Monitor the baby’s movements. A baby who doesn’t move often or stops moving may have a problem. If you notice any changes in your child’s movements, call your doctor right away.
  • Eat properly and healthily.
  • Fill up on energy. Rest helps mom feel better and might even help baby grow. The woman should sleep at least 8 hours at night and have an hour or two of rest in the afternoon
  • Adopt healthy habits: no smoking, alcohol or drugs.
Dr Kathryn Barlow

Kathryn Barlow is an OB/GYN doctor, which is the medical specialty that deals with the care of women's reproductive health, including pregnancy and childbirth.

Obstetricians provide care to women during pregnancy, labor, and delivery, while gynecologists focus on the health of the female reproductive system, including the ovaries, uterus, vagina, and breasts. OB/GYN doctors are trained to provide medical and surgical care for a wide range of conditions related to women's reproductive health.

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