By Cristina Mestre Ferrer BSc, MSc (embryologist) and Manuel Aparicio Caballero MD, MSc (gynecologist).
Last Update: 08/08/2016

Uneventful pregnancies last 40 weeks since the first day after the last menstruation. Therefore, newborns are classified in different groups according to their week of birth:

  • Preterm delivery: to be discussed later on.
  • Full term delivery: a birth that takes place between the weeks 37-42.
  • Post-term delivery: a birth taking place beyond the 42nd week.

What is a preterm birth?

A premature newborn, also known as preemie baby, is a baby who is born before the 37th week of gestation as a result of a delivery that takes place sooner than expected.

This is the case of 8-12% of pregnancies. Once the main causes of infant mortality are considered, nowadays the chances of survival are higher than ever: a fairly solid 80% of preterm newborns survive.

Those that are born between the 35th-37th week would not arguably be labeled as late prematures. It is unlikely that staying in ICU is necessary. Nonetheless, they must be observed in a way full-term newborns do not need.

We can tell a baby is born prematurely if the following features are identified if compared to a full term baby:

  • Big head, low weight (<2.5 kg) and poor muscle mass.
  • Smooth, thin, bright skin being almost traslucid, some veins and arteries are easy to distinguish.
  • Smooth and flexible ear cartilage.
  • Reddened feet and hand palms, poor crease-formation.
  • Presence of lanugo hair.
  • Low body temperature.
  • Breathing problems due to underdeveloped lungs and risk of pulmonary bleeding.
  • Weak weeping.
  • Newborn’s jaundice and risk of hypuglucaemia.
  • Weak suction and swallowing.
  • Underdeveloped genitalia: enlarged clitoris in girls and small scrotum in boys.

Signs of preterm labor

There are some symtpms that may warn the mother about a potential premature labor:

  • Having four or more contractions per hour before the 37th week.
  • Loss of amniotic fluid through the vagina. That may be indicating the premature rupture of the membranes that protect the unborn.
  • Feeling pressure in the pelvis or feeling of weight, a possible sign of the baby descending throughout the birth canal.
  • Menstrual cramping, abdominal, or back pain and even vaginal bleeding.

If the mother notices some of the following symptoms, she must go to the hospital immediately.

Preterm delivery complications

A fetus grows the most during the last 8 weeks of gestation. In the first 32 weeks, the baby grows up to a third of the total weight, and during the last 8 weeks, the unborn reaches the 2/3 left. The fetal organs have a similar pattern, being these last 8 weeks essential to achieve a full growth.

Premature newborns can suffer problems in the long term, but it is not possible to make prudent prediction of the clinical evolution of the baby relying only on the gestational age or weight at birth.

Thus, the smaller or underdeveloped the newborn is, the greater the risks are. The respiratory, nervous, digestive, renal, immunologic and visual sistems might be compromised, being the respiratory one of the most affected.

Premature baby care

To establish a set of measures, the newborn has to be assessed immediately. Usually, this kind of babies need to be tube-fed until breastfeed due to their suction and deglutition problems before 34th week. Also, the newborn may require assistance to overcome any respiratory deficiency, although it depends on the stage of prematurity of the newborn.

Therefore, an early baby cannot be taken care of at home, because the newborn needs specialized caring. He/she will have to stay in an incubator, which plays the role of a transitory uterus. It will keep the baby warm an under specific humidity conditions (30 °C, 80-90%).

The premature baby will be released in the moment assisted respiration and the warmth of the incubator are no longer required, being also necessary to have a proper weight and to suckle well.

Preterm birth prevention

In order for a preterm birth to be prevented, and for the baby to be born in due date, prospective mothers are recommended:

  • To be in good health condition prior to getting pregnant.
  • To receive prenatal cares as soon as possible, keeping them until the baby is born.

Sometimes, preterm birth can be treated with a drug that blocks uterine contractions. Such drug is the betamethasone, but most of the times these attempts to delay it turn out to be ineffective.

FAQs from users

Is a preterm birth more likely with twins?

By Manuel Aparicio Caballero MD, MSc (gynecologist).

According to the World Health Organization (WHO), a preterm birth occurs when the child is born before the week 37 of pregnancy. Some of the most common causes of preterm birth are:

  • Overdistention of the uterus: loss of tone in the uterine musculature that prevents this organ to recover its normal size.
  • Infection or uterine inflammation: certain bacteria can damage fetal membranes by causing its rupture and triggering a preterm birth. An infection that affects the uterus directly may lead to preterm birth as well.
  • Decidual bleeding: a type of vaginal bleeding that may occur while a woman is pregnant.

There exist many risk factors that can lead to premature birth, including obesity, high blood pressure, etc. A multiple pregnancy is one of these factors.

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Authors and contributors

 Cristina Mestre Ferrer
BSc, MSc
Bachelor's Degree in Biological Sciences, Genetics & Human Reproduction from the University of Valencia (UV). Master's Degree in Biotechnology of Human Assisted Reproduction from the UV and the Valencian Infertility Institute (IVI). Embryologist at IVI Barcelona. More information
 Manuel Aparicio Caballero
Bachelor's Degree in Medicine from the University of Murcia. Specialist in Obstetrics & Gynecology. Master's Degree in Human Reproduction from the King Juan Carlos University and the IVI. Currently, he is part of the team of Tahe Fertilidad (Murcia, Spain). More information
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  1. Featured
    virginia dunhill

    Hello, I’ve a history of preterm births and I’m 20 weeks pregnant now, worried that it happens to me too, although my pregnancy is going well!! My question is out of curiosity what is the survival rate of preterm babies at different pregnancy weeks? Guessing the earlier, the less chances.

    • Sandra FernándezBA, MA

      Hello virginia,

      Babies born earlier than 28 weeks have the most complications, mainly because most of them are born at extremely low birth weight, which requires treatment with oxygen, mechanical assistance to help them breather…

      Around 25% of these very preemie babies develop some serious lasting disabilities (e.g. behavioral problems, learning difficulties, etc.).

      I hope this helps,

      All the best

  2. Featured

    My baby delivered at 35 weeks by C-section. Her birth weight was 2 kg 240 gms. She was put on with antibiotics due to high total count. And also in photo therapy due to high total bilirubin. Now her weight is 2kg 100 gms. What should we do for our baby to gain weight? Please give me suggestions.

    • Sandra FernándezBA, MA

      Dear Vinilashree,

      As a premature baby gets stronger, they can start getting milk or formula, and the amount should be increased very slowly. This reduces the risk of an intestinal infection known as NEC (necrotizing enterocolitis).

      Also, premature babies find it harder to maintain the proper water balance in their bodies, and therefore become dehydrated or over-hydrated. In this sense, human milk from the baby’s mother is the best for babies born early or with very low birth weight.

      Supplements such as human milk fortifier are ideal for premature babies as they may need extra nutrients. This supplement gives them calories, iron, calcium, protein, vitamins, etc.

      I hope this helps,

      Best wishes