Narcotic medications cross the placenta to the baby after they enter the mother's blood stream. Pethidine can be detected in amniotic fluid within 30 minutes after the mother has received an injection into the muscle and within 2 minutes if given via the vein. Pethidine reaches peak concentrations equally in the mothers and baby's blood stream about an hour after it is administered, and starts to decline 2 hours after being given.
The drug is broken down by the mother's liver and excreted through her kidneys over a period of about 4 to 6 hours. This also reduces the levels in the baby's blood. If the baby is born before this time, the pethidine left in the baby's system must be broken down and excreted by the baby's liver and kidneys. This can take longer than an adult (up to 3 days) because their liver and kidneys are less mature than an adults and the blood levels are comparatively higher because the baby is smaller.
The fact that pethidine is detectable in a baby's system after the birth does not necessarily mean they will experience any noticeable effects. The following are some possible side effects that can happen for some babies, but are more likely to occur if the baby is born within 1 to 3 hours after the pethidine is given.
Baby's breathing at birth
Reduced CTG variability
Suck reflex and effects after the birth
Connecting with your baby
Baby's breathing at birth. Opiate medications are capable of suppressing the baby's desire to breathe at birth. If the baby is born within 1 to 3 hours of their mother having pethidine, about 1 in 4 can be affected in this way. A few of these babies will be slow to respond (not breathing themselves at birth), the caregiver will need to ventilate the baby's lungs with a special face mask and possibly give the baby an injection of naloxone (or Narcan) to reverse the effects of the pethidine. This can be given into the baby's muscle or vein or umbilical cord.