Why the third trimester of pregnancy is crucial

Share this article with other mums

The third trimester sees the completion of a significant number of developmental milestones for the foetus. A preterm labour compromises this development. With the help of Dr Malathi Sitaram, Consultant Neonatologist and Paediatrician at Parkway East Medical Centre, we help mums-to-be learn more about babies’ development during this period in order to understand why preterm babies are different from full term babies. This article is part of the DreamBig, an education series by Abbott, which aims to spread awareness on prematurity and help turn small starts into big futures.

abbott 5

The final trimester is often the hardest. You are almost there but not quite. You begin to become bigger and less mobile at a time when it seems like you have the most to do – finish off the nursery, finalize the hospital, organize handover at work, plan for confinement…the list seems endless. And while you are busy multi-tasking, your baby’s body is doing some serious work of its own.

Why is the third trimester crucial for my baby?

When your baby is 28 weeks old (the start of the third trimester) his organs are fully formed and visible on the ultrasound. However, while they may be clearly visible, his organs’ functions have not matured sufficiently for independent living. The full development of your baby’s brain and other vital organs such as lungs, eyes, heart, immune system, intestinal system, and kidneys takes places in this final term of your pregnancy.

Let’s explain a bit more. Take the baby’s lungs for example – an organ absolutely essential to breathing and therefore survival. It is not until the 34th week of gestation that certain proteins called surfactant are produced in your baby’s body. These surfactants are crucial in preventing the lungs from collapsing and facilitate independent breathing.

The speed of babies’ brain development accelerates rapidly during this time. The cerebral cortex (the brain center for thinking, remembering, feeling) enlarges rapidly, almost tripling in weight, and the brain’s formerly smooth surface becomes increasingly grooved and indented. However, in spite of these rapid developments, the cerebral cortex starts to function only around the time the full term baby is born.

Additionally, it is only in the third trimester that there is a high placental transfer of important nutrients, all of which are particularly needed to support the new born through the first six months of life.

In summary, premature babies would have these crucial developments compromised.


What is the definition of prematurity and do all preterm babies face the same complications?

Any infant born at less than the full 37 completed weeks of pregnancy is considered a preterm infant. Preterm babies face many challenges and the extent and gravity of the challenges depend on the number of completed weeks of gestation.

  • Extreme preterm babies are those born <28 weeks of gestation
  • Very preterm babies are those born between 28 to <32 weeks of gestation
  • Moderate to Late preterm babies are those born between 32 to- <37 weeks of gestation.

Being born early predisposes babies to a range of health complications as well as developmental delays. Complications could include bleeding in the brain or brain damage from lack of oxygen, infections, patent ductus arteriosus (a condition where a blood vessel in the heart is persistently open), chronic lung disease or necrotising enterocolitis (NEC – a serious condition in which there is severe damage to the intestines). Respiratory difficulties, feeding intolerance and infections are not uncommon; most very ill preterm infants may take up to 2-3 weeks just to regain their birth weight.

In such cases with more complications, babies have to spend the early days of their life in the NICU (Neonatal Intensive Care Units) wards, making it a very emotionally trying time for parents.


Click on the next page to find out how to calculate you preterm babies milestones.

Preemies Ages & Stages