fetal development

Fetal development

Pregnancy is traditionally divided into 3 trimesters.

First trimester 
  • The pregnancy implants within the womb.
  • Your baby starts to develop from an embryo into a tiny fetus and his/her vital organs form.
  • By week 14 the risk of miscarriage dramatically falls.
  • It is vitally important that during this first 3 – 4 months the developing fetus is not exposed to any harmful substances or drugs that could potentially have an adverse affect.
  • Nausea and vomiting are common, usually mornings, but symptoms can persist throughout the day. If you feel you are becoming dehydrated or there is excessive vomiting then it is important that you consult your doctor.
  • Nausea and vomiting in early pregnancy can sometimes indicate urinary tract infections or a multiple pregnancy. Once you have missed a period and have had a positive pregnancy test, arrange your booking antenatal visit - around 12 weeks gestation.
  • If you experience any bleeding in the early stages of pregnancy most hospitals now have access to an Early Pregnancy Unit specifically designed to deal with these complications.  If you are attending privately then you should contact your obstetrician as soon as any complications occur.
  • If you choose to, between 12 and 14 weeks gestation is when we screen for the more common chromosomal abnormalities such as Downs Syndrome. This involves a blood test for you and a special scan for your baby to look at the fat pad at the back of the baby’s neck otherwise called the nucal translucency.  We may decide to do further tests such as chorionvillus sampling or amniocentesis. These are designed to give a chromosome count for your baby and give a definitive diagnosis for you.
Second Trimester
  • Your tummy increases in size and you should start to feel fetal movements at around 20 weeks gestation, or earlier if this is not your first pregnancy.
  • About 20 weeks into your pregnancy your tummy will be at around the level of your umbilicus or tummy button.  Most hospitals now offer an anatomy screening scan at this stage. This scan is designed to look at your baby’s vital organs.
  • The 20 week anatomy scan will also identify the position of the placenta to ensure that it is not low lying. 
  • The position of the baby is not important at this point. Most babies of 20 weeks gestation are about the same size and there’s no indication yet of the final size of your baby.
  • It is important to remember that none of these scans are 100% accurate and they do not pick up all abnormalities e.g. some congenital heart malformations can be quite difficult to diagnose at this stage of pregnancy.
  • Towards the end of the second trimester your pregnancy will have just reached viability. This means that babies born at 25/26 weeks gestation, although extraordinarily premature, do have a chance of survival. Births at this time in pregnancy are unusual and often happen because of early onset pre-eclampsia or toxaemia of pregnancy. Keep in close contact with your doctor if you have symptoms of any kind – early detection leads to effective management.
  • At 28 weeks gestation your baby will have an estimated weight of somewhere between 700 grams and 1 kilo.  
  • If you have any family history of diabetes, a thyroid disease, you will be offered a glucose tolerance test at around 28 weeks gestation. Your visits will now become a little more frequent, possible visiting your GP and obstetrician alternately.
Third Trimester
  • Your baby puts on most of his/her weight. He/she is now fully formed and needs to prepare for delivery by developing subcutaneous fat. His/her lungs are also preparing for that first breath outside your womb.
  • Visits to your doctor will increase in frequency from now. Typically you will be seen at 30, 33, 36, 37, 38, 39, 40 and 41 weeks. At each your blood pressure and urine will be tested and you will be screened for pre-eclampsia and diabetes.
  • Your doctor or midwife will palpate your tummy to check your baby’s size and position, listen in to the fetal heart and assess the fluid around the baby.
  • Ultrasound scans may be done from time to time - to assess the fluid around the baby, the growth of the baby, the position of the placenta or to observe the baby’s movements.
  • Most women will attend antenatal education classes during the last third of pregnancy. It is very important that any issues or questions that arise as a result of these classes are brought to the attention of your doctor or midwife during your
    antenatal visits.
Planning for delivery
As you approach your due date you and your doctor or midwife will discuss plans in relation to your delivery. It is usually best to labour spontaneously unless there is a medical indication to induce labour, like –
  • prolonged pregnancy - in excess of 10 days beyond your due date.
  • your waters go before labour
  • a medical indication such as high blood pressure, concern over baby’s wellbeing or the function of the placenta.
If you baby is in the breech position – coming bottom first, your doctor will discuss with you the appropriate management of this situation which may include turning the baby (called external cephalic version) or elective caesarean section.

Elective caesarean sections are usually performed at 39 weeks. We choose this point and not earlier so your baby’s lungs are at their most mature. If any medical intervention such as induction of labour or caesarean section is required your doctor will explain this carefully to you prior to the event.

Labour and delivery
Most women will go into spontaneous labour between 37 and 41 weeks gestation. The onset of labour can vary in pattern. Once you are having regular labour pains, come to the hospital for evaluation to see if you are in labour. If your membranes have ruptured or there’s any bleeding, your hospital wants to have you in their care also, even if you don’t have contractions. Occasionally women who have been pregnant before can progress quite quickly in labour so should present to the hospital as soon as it is underway.

Pain relief in labour
There are a number of options in relation to pain relief in labour. Most of these will have been discussed with you at your antenatal classes. All options are available to you and easily accessible in almost all hospitals in the country. It is important, though, to go into labour with an open mind - you may manage your labour without pain relief.

It is a good idea to keep moving as much as is comfortable in the early stages of labour. Once the baby’s head is very low in the pelvis it is often quite uncomfortable to move around and people will often prefer to sit or lie down at this point. It is usually around this stage that you may choose to have an epidural and your midwife will call the anaesthetist immediately. However, there are many other methods of pain relief, such as Tens machine or Pethadine injection, usually given with a Stemetil injection to stop you feeling sick.

Provided progress in labour is normal, the majority of women will deliver assisted by the midwife and no medical intervention will be required. If progress in labour is slow and medical input is required this will be discussed with you in detail by either the team of doctors looking after you or your private consultant. If an instrumental delivery is required it will either be a ventouse or suction cup or a forceps delivery. The doctor looking after you will make a decision as to what is the most appropriate method of delivery based on the size of the baby, the position of the baby’s head and how low the head is in your pelvis. If an emergency caesarean section is required this is usually performed following the topping up of an epidural or insertion of a spinal anaesthetic.

Postnatal stay
Your postnatal stay will usually be 2/3 days or 4/5 days if you’ve delivered by caesarean section. Most hospitals now have an early transfer home facility. Once you have been discharged one of the hospital midwives will call to you to your home to ensure that everything is going well in the postnatal period.

If you have any concerns in relation to your pregnancy do not hesitate to contact the doctors on call or your own consultant through the hospital if the need arises. After delivery you are still a patient of the hospital for the first 6 weeks after you give birth.