Introduction

Hypoxia is defined as low levels of oxygen in the blood. Oxygen is vital for human life as all body systems utilise oxygen for energy production and function. During fetal development inside the womb, fetal tissues also utilise oxygen to produce energy for the growth and development of different organs and tissues till birth. Oxygen is delivered to the developing fetus from the mother via the placenta. Thus, a huge reduction of oxygen or hypoxia will greatly impact fetal development, outcome and survival. Worldwide, fetal hypoxia represents 23% of perinatal mortality.¹ Understanding the causes and the impact of hypoxia on the developing fetus is important for preventing hypoxia and managing it promptly.

Causes and types of hypoxia in fetal development  

To understand fetal hypoxia, we should contemplate the source of oxygen for the fetus, the mechanism of oxygen delivery to the fetus and the fetus itself. Then, we should consider maternal factors, placental factors and fetal factors.

Maternal factors contributing to hypoxia 

Since the fetus depends on its oxygen supply from its mother, maternal hypoxia will eventually lead to fetal hypoxia. Here are some major causes of maternal hypoxia:

Cardiovascular diseases 

Maternal cardiovascular diseases can greatly affect fetal conditions. The birth parent’s heart is responsible for pumping blood to maternal tissues and organs through blood vessels and to the developing fetus in the womb. Any disease or condition affecting the birth parent’s cardiovascular system can affect the fetus. The most common cardiovascular conditions of the mother that can affect the fetus include: hypertensive disorders, congenital heart diseases and cardiomyopathies.

Living in high altitude

 At high altitudes, the partial pressure of oxygen in the air is considerably low, this can result in a reduced amount of oxygen in the blood; a condition called high-altitude hypoxia. This condition can affect the mother and the fetus and increases the risks of perinatal mortality and morbidity.

Pulmonary diseases

Pulmonary conditions such as chronic obstructive pulmonary diseases, asthma, and pneumonia can lead to fetal hypoxia by reducing the oxygen content of maternal blood and impairing the exchange of respiratory gases at the placental level.

Maternal hematologic disorders

Maternal haematological disorders can directly affect the transfer of oxygen to the embryo. Oxygen is transported by haemoglobin which is present in the red blood cells. Any disorder affecting the haemoglobin of the mother can affect the oxygen delivered to the fetus. A common haematological disorder of pregnancy is anemia which is mostly related to the mother’s diet. 

Another common haemoglobinopathy is sickle cell anaemia which can lead to complications in the fetus such as intrauterine growth retardation, preterm delivery and prematurity.

Placental factors 

The main function of the placenta is to provide the developing fetus with oxygen and nutrients derived from maternal blood. Hence any factor affecting the normal function of the placenta can affect the oxygen delivery to the fetus and can lead to fetal hypoxia. Among the placental factors contributing to fetal hypoxia, it's worth noting pre-eclampsia, a condition caused by abnormal placentation which leads to multiple organ dysfunction. It is characterised by elevated blood pressure, and protein in urine and may also present by edema or fluid retention in the body. Pre-eclampsia affects the mother and the fetus and depending on its severity may lead to non-negligible fetal hypoxia, intrauterine growth retardation, prematurity and fetal demise.

Fetal factors

The fetus can contribute to its own hypoxia as well. Here are the main fetal factors that can contribute significantly to fetal hypoxia:

• Congenital heart defects: can lead to impaired oxygen distribution within the fetus and may lead to chronic fetal hypoxia
• Fetal anaemia: the oxygen-carrying capacity of the fetus will lessen and hypoxia may supersede
• Fetal infections: during severe infections, there is a high oxygen demand and may lead to fetal hypoxia

Effects of hypoxia on specific fetal organs

Brain development and neurological outcomes

Of all body organs, the brain has the highest oxygen demand for its metabolism. Therefore, it is sensitive to oxygen levels in the blood. Depending on the timing and duration of hypoxia, the effects on fetal brain development may vary and the neurological impact can be significant and long-lasting.² Prolonged hypoxia to the brain will affect the brain cells and lead to poor neurodevelopmental outcomes such as cerebral palsy, autism spectrum disorders and epilepsy. The brain also controls behaviour, memory and learning, motor development and much more. This may later lead to neuropsychiatric disorders such as anxiety and depression, learning difficulties and delays in reaching motor milestones. Brain affection will affect the life quality of the newborn.

Cardiovascular system development

Hypoxia can have an important effect on the cardiovascular system development of the fetus. During fetal life, in the event of hypoxia, the fetus adapts strategies to cope with the diminished oxygenation notably by decreasing oxygen consumption and increasing its extraction from the placenta. Acute hypoxia will also lead to a reduction in the fetal heart rate.³

More of the blood is preserved in the brain and heart at the expense of other non-essential organs for fetal survival. In the long term, fetal hypoxia may cause cardiac remodelling and may lead to an increased risk of hypertension and heart diseases later in life. 

Pulmonary development and respiratory outcomes

Fetal hypoxia can also impact the fetal respiratory system and subsequent respiratory outcomes. Short-term and long-term effects of hypoxia on the fetus depend on the duration, severity and gestational age during which hypoxia occurred. Common consequences of fetal hypoxia on the respiratory system are respiratory distress and pulmonary hypertension.

Clinical implications and monitoring

The clinical implications and fetal monitoring for hypoxia are of utmost importance during prenatal and intrapartum care for good outcomes.

Methods for detecting fetal hypoxia 

There are several methods for detecting fetal hypoxia. Antenatally, regular prenatal checkups, ultrasounds for fetal assessment and Doppler studies can help detect any abnormal conditions that can lead to fetal hypoxia. In addition to this, several other methods can be used intrapartum to help detect fetal hypoxia and act accordingly. This includes:

Cardiotocogram

This is a device used in a healthcare setting to monitor fetal heart rate and maternal contractions. It can also detect atypical patterns that may indicate fetal hypoxia.

Fetal scalp blood sampling

In this technique, a healthcare professional takes some blood from the fetal scalp, and the skin surrounding the fetal head bone and examines it to detect the pH and lactate which can indicate whether the fetus is hypoxic or not.⁴

Intervention strategies to mitigate hypoxic conditions

Quick recognition and appropriate interventions are paramount to prevent early and long-term complications from fetal hypoxia. Here are a few strategies that can help mitigate hypoxic conditions of the fetus:

Administration of oxygen to the mother 

By administering oxygen to the mother, we also help the fetus get more oxygen from the mother’s blood which can help to improve fetal hypoxia to some extent.

Changing maternal position to her left lateral position 

This will improve maternal blood circulation by decompressing the mother’s blood vessels which can be compressed by the gravid uterus. 

Treatment of underlying maternal conditions

Treating maternal conditions which are the causes of fetal hypoxia such as maternal diabetes, high blood pressure, infection, pre-eclampsia and eclampsia.

Operative delivery

This can be an emergency cesarean section to save the baby or assisted delivery using forceps or a vacuum during delivery.

Long-term monitoring and follow-up of infants exposed to fetal hypoxia

Long-term monitoring and follow-up of infants exposed to fetal hypoxia is necessary to detect early complications and manage them accordingly. Immediately after birth, a paediatrician should examine the newborn and manage any abnormality present. Abnormalities should also be recorded for further follow-up.pecial consideration for hypoxic ischemic encephalopathy should be given as it can lead to long-term neurological disorders that may include mental impairment and cerebral palsy.⁵

Infants exposed to antenatal or intrapartum hypoxia should get regular check-ups by paediatricians and other healthcare professionals such as neurologists and developmental specialists focusing mainly on their neurodevelopmental outcomes such as their cognitive functions, speech and language development, motor skills and social and behavioural skills.

Summary

Fetal hypoxia is significant in obstetrics and paediatrics as it has the potential for serious short-term and long-term consequences on fetal development. Depending on the timing, severity and duration of hypoxia, the impact of impaired oxygenation on the developing fetus can be mild, transient or severe long-standing disabilities. Early detection remains crucial for better outcomes. With proper management with a multidisciplinary approach involving specialists such as obstetricians, neonatologists and paediatricians, in addition to the advanced monitoring techniques, many affected infants can have positive outcomes. As the consequences of fetal hypoxia are serious, ongoing research for a better understanding of the mechanisms of fetal hypoxia and improving its prevention and treatment strategies should be encouraged to get more favourable outcomes for affected babies and their families.