Polyhydramnios And Macrosomia

Introduction

Polyhydramnios is the presence of excess amniotic fluid. It is a rare complication of pregnancy that is seen in about 1% of pregnancies. The cause is usually unknown in the majority of cases, however, it could be due to problems from the mother or baby. 

Macrosomia is used to describe birth weight beyond 4000g or 4500g regardless of the gestation age. When polyhydramnios coexists with macrosomia, the suspicion of diabetes in pregnancy should be high. Both conditions can lead to unfavourable pregnancy outcomes if not well managed.

How do polyhydramnios develop?

The amniotic fluid provides a cushion for the developing baby. It is produced through secretions from the baby’s lungs and skin and also through the coverings of the amniotic sac. The major source of production is the baby’s urine. It is majorly removed through swallowing by the baby. ¹ There is a balance between production and removal and this keeps the fluid within the normal range. Any condition that disturbs this balance leads to increased or decreased amniotic fluid volume. These conditions are usually those that affect swallowing or urination. 

Causes and risk factors for polyhydramnios and macrosomia

Polyhydramnios

Polyhydramnios can be idiopathic (of unknown cause). However, in some instances, there may be risk factors or known causes.^2,3 These could be due to problems concerning the mother or the baby.

Problems concerning the mother 

• Diabetes (disease associated with elevated blood sugar) 
• Rhesus isoimmunization (when the mother develops antibodies that attack the baby’s blood cells) 

Problems concerning the baby

Any problem that prevents swallowing of the amniotic fluid or increase in urination can cause polyhydramnios.^1,3

These include:

• Problems with the digestive tract like oesophageal or duodenal atresia
• Anencephaly or any other central nervous system disorder
• Viral or bacterial infections in the baby – including diseases such as syphilis or cytomegalovirus transferred from the mother to the baby
• Anaemia (low red blood cell percentage) in the baby
• Congenital problems characterised by defects in the anterior abdominal wall: e.g., omphalocele, gastroschisis
• Muscle weakness disorders like myotonic dystrophy
• Neck or chest region tumour or mass in the baby
• Genetic disorders, such as Down’s syndrome
• Any condition associated with increased urination by the baby e.g., Bartter syndrome
• Twin pregnancy especially when there is a twin-twin transfusion in identical twin pregnancies

Macrosomia

Causes of macrosomia could also be from the mother or baby, including: ^4,5,6 

From the mother

• Previous history of macrosomia
• Diabetes in the mother
• Maternal obesity
• Excessive maternal weight gain in pregnancy
• Increasing number of pregnancies (multiparity)

From the baby

• Prolonged pregnancy
• Assigned male at birth baby
• Some congenital diseases like Beckwith-Wiedemann's syndrome

The link between polyhydramnios and macrosomia

Maternal diabetes causes both polyhydramnios and macrosomia. Pregnant women diagnosed with both conditions should be screened for diabetes in pregnancy. However, there may be cases in which both conditions are present with no abnormality in blood sugar levels.⁷

Diabetes in pregnancy can be of two forms:

• Pregestational diabetes (diabetes that developed before pregnancy)
• Gestational diabetes (diabetes that developed or was first recognised in pregnancy)

Diabetes causes polyhydramnios due to the excessive transfer of sugar to the baby. This leads to increased release of insulin in the baby. The insulin leads to increased deposition of fat especially on the trunk of the baby leading to macrosomia.

The excess sugar in the baby leads to increased urine production in the baby leading to increased amniotic fluid volume.³ 

The diagnosis is made with the blood sugar level:

• A blood sugar of greater than 7 mmo/l is suggestive of preexisting diabetes
• Abnormal values of the Oral Glucose Tolerance Test are used to diagnose gestational diabetes

There are so many criteria for the Oral Glucose Tolerance Test but the World Health Organization (WHO) criteria is the most widely used.

With the WHO criteria gestational diabetes is diagnosed if any one of these values is abnormal after a 75 grams of glucose intake:

• Fasting blood glucose of 5.1-6.9 mmol/l (92 -125 mg/dl) 
• One hour post 75 g oral glucose load sugar level that is greater than 10.0 mmol/l (180 mg/dl)
• Two-hour post 75 g oral glucose load sugar level of  8.5 – 11.0 mmol/l (153-199 mg/dl)

Clinical presentation of polyhydramnios and macrosomia

Mild polyhydramnios usually do not present with any symptoms. It can only be diagnosed with an ultrasound scan.

Severe polyhydramnios can manifest as:

• The rapid increase in the size of the abdomen
• Abdominal pain
• Tightness in the abdomen
• Difficulty breathing
• Heartburn
• Constipation
• Swollen feet

On examination, the following may be observed:

• The fundal height – the measurement of the size of the pregnant uterus (womb) greater than the gestational age (age of the pregnancy in weeks)
• Shiny abdomen
• Difficulty in palpating the baby through the abdomen
• Difficulty in hearing the baby’s heart rate

These symptoms are not exclusive to polyhydramnios as other conditions in pregnancy may cause similar symptoms. The diagnosis must be confirmed with an ultrasound.

Macrosomia can also be suspected in pregnancy if the size of the pregnant womb is larger than the age of the pregnancy. The precise diagnosis however can only be made at birth.

Diagnosis of polyhydramnios and macrosomia

Polyhydramnios can be diagnosed through an ultrasound measurement.^8,9 The ultrasound values that indicate polyhydramnios are:

• An amniotic fluid index greater than 25 cm
• A maximum vertical pocket of amniotic fluid greater than 8 cm
• Amniotic fluid greater than 2000 mL at any gestational age

In addition to confirming the diagnosis, an ultrasound can be used to check the condition of the baby by checking the:

• Baby’s well-being (Biophysical profile)
• Organs of the baby for anomalies (anomaly scan)

Macrosomia can be suspected on ultrasound when the baby's estimated weight is greater than what is expected at the calculated gestational age.

Management of polyhydramnios and macrosomia

The management of polyhydramnios is dependent on:

• The severity of the condition
• The age of the pregnancy
• The state of the baby

Mild polyhydramnios

Mild polyhydramnios does not usually require any treatment. However early delivery between 39 to 40  weeks of the pregnancy is necessary. If the patient has an underlying cause like diabetes, it needs to be treated and that may resolve the fluid accumulation.

Severe polyhydramnios

The treatment depends on the age of the pregnancy and the condition of the baby and mother. Delivery may be the option of management if:

• If the baby is mature (up to 37 weeks)
• If there are problems with the baby’s breathing or heart rate

If the mother has severe discomfort from the condition and the baby is not yet matured reduction of the amniotic fluid can be achieved through:

• Amnioreduction – The reduction of the amniotic fluid by draining it with a catheter. The risk of this procedure includes premature contractions. Detachment of the placenta and rupture of the membranes (breakage of the water sac) could occur 
• Use of drugs like indomethacin – This is a non-steroidal anti-inflammatory drug (NSAID) It is useful in the reduction of amniotic fluid volume within one week of use

The management of suspected macrosomia include:

• Antenatal monitoring: Serial ultrasounds to monitor the baby’s growth and amniotic fluid levels
• Blood sugar level: Ensuring optimal management of maternal diabetes to prevent excessive fetal growth
• Delivery planning: Determining early induction of labour or elective cesarean delivery (C-section) in cases of suspected macrosomia, especially if the estimated foetal weight is significantly high

For the patient with polyhydramnios and macrosomia who has diabetes in pregnancy, there is a need for multidisciplinary management. This would involve:

• Obstetricians (doctors who take care of pregnant women)
• Endocrinologists (doctors who deal with hormonal problems)
• Dieticians (health professionals who deal with nutrition)
• Neonatologists and paediatricians (doctors who take care of babies)

At delivery, precautions should be taken to prevent postpartum haemorrhage in the mother by ensuring active management of the third stage of labour.

The baby should also be reviewed and monitored by specialised doctors to detect and manage complications that may arise.

Complications

 The complications of polyhydramnios include:

• Preterm labour and delivery
• Premature rupture of membranes (PROM) – early water breaking
• Placental abruption (premature separation of the placenta)
• Prolapse of the umbilical cord
• Abnormal position of the baby in the womb
• Increased risk of cesarean delivery
• Increased risk of bleeding after birth (postpartum haemorrhage)
• Long-term complications like pelvic organ prolapse and incontinence

Complications of macrosomia include:

• Obstructed labour
• Injuries to the mother during delivery
• Postpartum haemorrhage (bleeding after birth)
• Increased risk of caesarean delivery
• Birth injuries to the baby
• Birth asphyxia (inability of the baby to cry at birth)
• Newborn problems like hypoglycaemia (reduced blood sugar), hypocalcaemia, hypoglycaemia, breathing problems and jaundice
• Long-term complications like increased risk of obesity and metabolic syndrome in adulthood

Conclusion

Polyhydramnios and macrosomia are serious conditions that must be carefully managed to guarantee the safety of both the mother and the baby. Understanding the causes, diagnosis, consequences, and management options for these disorders allows healthcare providers to make more informed decisions and give the best available care. 

Regular antenatal checkups and personalised care regimens are critical in managing pregnancies complicated by polyhydramnios and macrosomia.

FAQs

What is the biggest risk of polyhydramnios?

Polyhydramnios has many risks but the challenge of delivering a premature baby is quite significant. This is because of the high risk of death and other complications in premature babies.

What is the best time of delivery when there are polyhydramnios?

Your doctor would determine the best time for delivery based on the age of the pregnancy, your condition and the condition of your baby.

Are polyhydramnios and macrosomia always associated with diabetes?

Although diabetes causes both polyhydramnios and macrosomia, however, diabetes is not always present when there are polyhydramnios and macrosomia.

What birth defects are caused by polyhydramnios?

Polyhydramnios does not cause birth defects, however, some birth defects like anencephaly, Down’s syndrome and oesophageal atresia can cause polyhydramnios.