These are my notes from reading Lise Elliot’s What’s Going On in There?.
“How Birth Affects the Brain”.
This chapter describes the effects on the baby of labour, birth, and the drugs used in childbirth. The drugs, while beneficial for the mother, are probably overused from the baby’s point of view.
In general women today are quite careful about what they put in their bodies during pregnancy, so it can seem a little odd that many lose all caution on the last day of gestation, just when the baby is making the difficult transition to surviving on his own and will no longer have the benefit of his mother’s circulation to clear drugs out of his system. […] All analgesics and anesthetics used in childbirth are serious controlled substances, in another league entirely from the occasional Tylenol or antihistamine that many women worry about during pregnancy.
A few interesting facts I learned:
- The birth itself may be triggered by the brain of the baby. That’s how it works in some other species.
- Stress hormones, which speed up breathing and heart rate in adults, have the opposite effect in babies, which helps them conserve oxygen during birth. They also give some last-minute help to mature baby’s lungs.
- For some reason, they don’t use nitrous oxide for pain relief in the US – it isn’t even mentioned in this chapter!
Birth is possibly the most traumatic event we experience, and the brain is affected the most, because the head is large relative to the rest of the body, and comes first. Besides physical trauma, labour can also hinder the brain’s oxygen supply, which is the greatest danger to the baby at birth.
It is possible that birth itself is triggered by the brain of the fetus. (That’s how it works in sheep, where it has been studied most thoroughly.) The brain of the lamb fetus releases hormones which kick off other hormones (cortisol) which travel to the placenta and prepare it for the birth. In fact cortisol levels rise already through the last 3 weeks of pregnancy and help prepare the fetus’s organs for life outside the womb. The hormones involved are different in primates but the mechanism is probably similar.
During birth, each contraction compresses the baby’s head and body, and temporarily reduces blood flow to the placenta and the umbilical cord. This increases the levels of hormones that are associated with stress reactions in adults (high heart rate etc). In an infant they have an opposite effect, slowing the heart and the breathing. This helps the baby conserve energy and oxygen. The hormone levels remain high for 30 minutes after birth and then decline. This stress (which the baby doesn’t get in a C-section, unless it is preceded by several hours of labour) is very good for baby’s breathing and contributes to lung maturation. The hormones also seem to stimulate the nervous system – newborns are more alert during the first 2 hours of life than for many days thereafter.
The baby’s head can be squeezed and molded somewhat without suffering damage. The fontanels allow the bones to slide without harming the brain. Sometimes the head does get damaged. The most common form of damage is bleeding between the skull and the scalp, which leads to swelling (bumps on the head). The bumps are no threat to the brain and almost always disappear within 3 months.
While the brain is well protected, the nerves outside the skull and the spinal cord are more exposed. Sometimes the nerves leading to the shoulder and arms (which exit the spinal cord near the neck) or to the face can be damaged if the shoulder gets stuck or the jaw is squeezed hard against mother’s tailbone. Neurons outside the spinal cord are capable of regrowing a path to their target, so this normally heals within months. Sometimes head trauma can tear the outer membrane of the brain, which can lead to permanent brain damage. Likewise if the spinal cord is damaged, the effects (cerebral palsy or paralysis) are irreversible. The risk of spinal cord injury is greatest in breech babies, if the head gets caught.
The greatest danger is that the baby does not get enough oxygen, which can happen if the umbilical cord gets compressed or the placenta is damaged. Experiments with monkey fetuses have shown that total lack of blood flow can be tolerated for up to 8 minutes. 10 to 20 minutes leads to brain damage, and any more leads to death. Partial oxygen deprivation can be tolerated for between 1 to 3 hours without evidence of harm. While 2% of babies suffer some shortage of oxygen, only 1 in 1000 suffers significant brain damage.
The greatest concern is cerebral palsy (CP), which is a general term for disorders of movement or posture caused by brain damage. It does not get worse as the child grows up, but it may look as it does, because it isn’t always evident until later – newborns are capable of few voluntary movements. Because of how blood vessels develop in the brain, the first area to be damaged by blood pressure in the brain is the motor cortex (in particular areas controlling the legs and spine) followed by areas for vision and hearing. Only 10-20% of CP cases are caused by birth damage. The rest are caused before birth – sometimes because of mother’s health problems such as high blood pressure, but more often they are completely unpredictable.
Most interventions and technical innovations in modern obstetrics are aimed at preventing brain damage from hypoxia. Unfortunately there is little evidence that the measures have reduced the number of children born with CP or other disorders.
A very common procedure is monitoring the fetus’s heartbeat, either through the mother’s belly or directly through the baby’s scalp. In principle this provides useful information. But because the heart rate is only an indirect measure for the facts that really matter (blood pressure, oxygen to carbon dioxide ratio) it cannot be known for sure that a certain heart rate pattern means that the baby is in distress. Also, interpreting the patterns is very subjective and practitioners often disagree.
Studies have shown that fetal monitoring has not improved the baby’s chances of being born healthy. Monitored babies are just as likely to die, to need intensive care or to develop CP. And in one study the false-positive rate for predicting CP based on heart rate monitoring was 99.8%. This would be OK if diagnoses of fetal distress didn’t lead to C-sections, which can lead to serious complications.
The fetus can move around in the womb through most of pregnancy. Space gets tight in the last few weeks and babies then generally work themselves into the best position for birth: head down. Some don’t, and end up breech. Breech presentation is associated with increased risk for physical trauma (the head can get caught) and of asphyxia (the head comes out after the cord, so the baby cannot start breathing if there is trouble with the cord).
Because of this, most breech babies are delivered through C-section. This has led to fewer cases of brain damage. But C-section is really only necessary for maybe a third of breech babies – not if the baby’s position is otherwise straightforward and it is of average size. Nevertheless many doctors don’t like to deliver breech babies vaginally. Luckily there is an alternative – turning the baby from breech to head-down, before birth. This procedure (external cephalic version) succeeds in 50-75% of cases.
Forceps use is associated with higher incidence of birth trauma and serious complications. However this may be due not to forceps use itself, but to the condition which made it necessary. Compared to C-section, forceps use does not appear to be more dangerous. However doctors have become more cautious and tend to opt for C-sections.
The vast majority of American women receive some sort of medication during childbirth to relieve pain. Opinions differ about how much the drugs affect the baby’s brain. Pediatricians tend to be most concerned; anesthesiologists least; obstetricians fall somewhere in between. In some cases anesthesia is necessary (C-sections) or makes childbirth easier. In some cases pain can frighten the woman, slowing down labour. Anesthesia may also protect the brain in difficult deliveries, by slowing down the baby’s brain metabolism. But at the same time, all pain-relieving drugs used in childbirth are serious drugs. While women are careful about what they put in their bodies during pregnancy, they seem to be much less careful during birth.
Systemic analgesics or pain relief drugs that reach the entire body are the most used painkillers in childbirth in the US. These are mostly opiates. These cross the placenta easily and reach almost the same concentration in the fetus’s blood as in the mother’s. In the mother’s body it takes an hour for the drug to reach peak concentration, and about 4 hours before the concentration goes down significantly. If the baby is born before the peak is reached, it doesn’t get much of the drug. If it is born after the 4 hours, the mother’s circulation helps clear it from the baby’s body. If it is born between 1 and 4 hours after the drug is injected, it gets the full concentration, and the baby body has to break down much of the drug. While this takes 4 hours in an adult body, it can take up to 20 in a baby’s immature body. And the breakdown byproducts can take days to clear. The most serious effect on the baby is breathing problems, which can be countered by another drug. Babies exposed to opiates during birth also tend to be sleepier and less active, and may have difficulty with breast-feeding because the suckling reflex is suppressed. It is unclear whether there are longer-lasting effects.
(Note by HT: in both Sweden and England nitrous oxide is the most used systemic analgesic, precisely because the dangers of opiates. It is not broken down by the body but dissipates quickly from the blood through the lungs. It also does not suppress baby’s breathing. However it doesn’t work for all women.)
Epidural anesthesia blocks pain signals from the lower half of the body only. A catheter is inserted between two vertebrae in the spine, so that its end is just outside the membrane surrounding the spinal cord. Pain-killing drugs are administered through the catheter. The mother feels virtually no pain, but loses little of the mobility in legs and pelvis, which explains why epidurals are so widely used.
The drugs can partly escape the epidural space and into the bloodstream of mother and fetus, but the amounts will be smaller than when the drugs are used systemically. Studies disagree about the effect of these drugs on the baby, but they are probably insignificant for most babies.
Epidurals also affect the baby more indirectly. The most common side effect for the mother is lowered blood pressure. If it drops too low, the fetus will get too little oxygen. This is prevented by giving the mother fluids through an IV, and if that is not enough, another drug is used to counteract this.
Studies have also shown that women who get an epidural have longer labours than those who get systemic analgesia. They are more likely to be diagnosed with “failure of labour to progress”, and more likely to have C-sections. However there is vehement disagreement about cause and effect here. An epidural slows labour, because it relaxes the pelvic muscles, reduces the mother’s urge to push, and may repress the baby’s own movements that help position him for birth. But it is also possible that women who get epidurals do so because their labour is already more difficult (because the baby is larger or less favourably positioned).
General anesthesia is rarely used for birth nowadays – only if a C-section is needed, and there is not enough time for an epidural. Even though the baby is usually delivered within 3 minutes, the drugs have time to cross the placenta and affect the baby. The baby tends to be less active and less alert, their reflexes may be disturbed, and they may have trouble breast-feeding for several days. In fact it is a paradox that a baby born to a sleeping mother can be awake at all.