What is a premature baby? – Causes, care and complications

By (gynecologist), (gynecologist), (embryologist), (embryologist), (embryologist) and (fertility counselor).
Last Update: 12/16/2022

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.

However, when preterm labor occurs, special care of the baby is important. These babies may have immature lungs, which can cause breathing problems. In addition, premature babies have a lower body temperature and a weak cry, among other characteristics.

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.

What characterizes a premature baby?

Primarily, a premature infant differs from a full-term infant by the following characteristics:

  • 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.

In addition, the joints of premature babies are much looser than those of full-term babies. The movement of premature babies is less and may sometimes be in the form of jerking.

If delivery occurs before 32 weeks gestation, the baby may have transient hypertonia. This is an increase in muscle tone from head to toe.

Problems of a premature baby

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.

Other complications in the premature infant

Complications in babies born before their due date will depend on the exact time of delivery. The earlier the preterm birth occurs, the worse the fetal consequences will be since the baby will be less mature.

The following are some of the complications that can arise in premature babies:

Respiratory distress syndrome
also known as respiratory distress syndrome. This syndrome is characterized by closed alveoli due to the lack of surfactant, that is, the substance that coats the alveoli and whose function is to reduce surface tension so that they do not collapse.
is shortness of breath for 20 seconds or more. Apnea may also be associated with bradycardia.
Intraventricular hemorrhage
usually occurs in infants who do not reach a weight of more than 1.5 kg. The prognosis will depend on the degree of extension of the hemorrhage.
Arterial hypotension
es decir, el recién nacido tendrá baja la tensión arterial.

In addition to all these complications, premature babies are more prone to infections. Their defense mechanisms are not fully developed, so there is a higher risk of pneumonia and urinary tract infections.

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 M.D., M.Sc. (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.

Is there an increased risk of preterm delivery in IVF?

By Victoria Rey Caballero M.D., M.Sc. (gynecologist).

There are several scientific studies that have shown a slightly increased risk of preterm delivery in children conceived by in vitro fertilization (IVF) compared to children conceived naturally.

It is also known that many of the causes of infertility in women who require IVF are the same causes that have a higher risk of preterm delivery. This is the example of diabetes, thyroid problems, alterations in the coagulation system, immune disorders, adenomyosis, fibroids, advanced age, etc.

What should a premature baby be fed?

By Victoria Moliner BSc, MSc (embryologist).

According to experts, breast milk is the best food for newborns, especially premature infants. However, in the case of premature babies, since they cannot suckle properly, it is necessary to introduce food through nasogastric or stomach tubes. Sometimes, due to the sequelae of prematurity at birth, it is necessary to supplement their diet with iron.

What are the best stimulation exercises for premature babies?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

First of all, it is important to know the baby's corrected age, i.e. the number of months he/she would have been if he/she had been born on the due date and not before. In this way, it is possible to know the moment of development in which the baby is in order to start with the early stimulation.

Before carrying out the exercises discussed in this article, it is necessary to practice the following activities with premature babies:

  • Infant massage: this consists of holding each of the parts of the baby's body with your hands without moving them, just so that the baby feels the contact and trying to transmit relaxation and tranquility.
  • Therapeutic touch: this involves massaging and caressing the baby but without touching him, keeping a distance of about 5-10 cm.
  • Place the baby naked on the mother's or father's chest, between the clothes and the bare skin, maintaining the maternal-filial bond. This promotes the production of breast milk and helps regulate the baby's temperature and heart and respiratory rate.

Can a premature baby be delivered naturally?

By Victoria Moliner BSc, MSc (embryologist).

Yes, it is possible for an early delivery to occur through the vaginal canal. That is, it is not always necessary to have a cesarean section in the case of preterm labor.

What is corrected age in premature infants?

By Marta Barranquero Gómez B.Sc., M.Sc. (embryologist).

The corrected age is the time the baby would have had if delivery had occurred at 40 weeks gestation. This age is recommended when you want to evaluate the physical and psychomotor development of the baby.

It is calculated by subtracting the weeks of prematurity from the baby's weeks since birth. For example, if the birth occurs in the 32nd week of pregnancy, the baby would be 8 weeks, that is, 2 months premature. If the baby is now 4 months old (16 weeks), the corrected age would be 4 minus 2 months.

Can a 23-week premature baby survive?

By Marta Barranquero Gómez B.Sc., M.Sc. (embryologist).

It is possible. However, the earlier in the pregnancy the baby is born, the more immature it will be. Therefore, the more premature the baby is, the less likely it is to survive.

The percentage of babies who have been able to survive despite being born at 22-23 weeks of gestation is quite low, but not zero.

Suggested readings

If you would like to learn more about the possible signs of preterm labor, you can visit this article: What Is Preterm Birth? - Signs, Causes & Treatment.

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Alexander Humberg, Ingmar Fortmann, Bastian Siller, Matthias Volkmar Kopp, Egbert Herting, Wolfgang Göpel, Christoph Härtel; German Neonatal Network, German Center for Lung Research and Priming Immunity at the beginning of life (PRIMAL) Consortium. Preterm birth and sustained inflammation: consequences for the neonate. Semin Immunopathol. 2020 Aug;42(4):451-468. doi: 10.1007/s00281-020-00803-2 (View)

Heather A Frey, Mark A Klebanoff. The epidemiology, etiology, and costs of preterm birth. Semin Fetal Neonatal Med. 2016 Apr;21(2):68-73. doi: 10.1016/j.siny.2015.12.011 (View)

Joshua P Vogel, Saifon Chawanpaiboon, Ann-Beth Moller, Kanokwaroon Watananirun, Mercedes Bonet, Pisake Lumbiganon. The global epidemiology of preterm birth. Best Pract Res Clin Obstet Gynaecol. 2018 Oct;52:3-12 (View)

Kelsie Moroney. Family reflections: premature baby. Pediatr Res. 2021 Feb;89(3):705-706. doi: 10.1038/s41390-020-01296-3. Epub 2020 Dec 8 (View)

FAQs from users: 'Is a preterm birth more likely with twins?', 'Is there an increased risk of preterm delivery in IVF?', 'What should a premature baby be fed?', 'What are the best stimulation exercises for premature babies?', 'Can a premature baby be delivered naturally?', 'What is corrected age in premature infants?' and 'Can a 23-week premature baby survive?'.

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Authors and contributors

 Victoria  Rey Caballero
Victoria Rey Caballero
M.D., M.Sc.
Dr. Victoria Rey Caballero has a degree in Medicine and Surgery from the University of Seville. She is also an expert in Health Informatics and Telemedicine from the UNED and has a diploma in Neonatal Cardiopulmonary Resuscitation. In addition, Dr. Rey has a master's degree in hospital management from the University of Alcalá de Henares. More information about Victoria Rey Caballero
Licence number: 41/14915
 Manuel Aparicio Caballero
Manuel Aparicio Caballero
M.D., M.Sc.
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. More information about Manuel Aparicio Caballero
License: 303008030
 Marta Barranquero Gómez
Marta Barranquero Gómez
B.Sc., M.Sc.
Graduated in Biochemistry and Biomedical Sciences by the University of Valencia (UV) and specialized in Assisted Reproduction by the University of Alcalá de Henares (UAH) in collaboration with Ginefiv and in Clinical Genetics by the University of Alcalá de Henares (UAH). More information about Marta Barranquero Gómez
License: 3316-CV
 Victoria Moliner
Victoria Moliner
BSc, MSc
Degree in Biochemistry and Biomedical Sciences from the University of Valencia (UV). Master's Degree in Biotechnology of Human Assisted Reproduction from the UV and the Valencian Infertility Institute (IVI). Presently, she works as a Research Biologist. More information about Victoria Moliner
 Zaira Salvador
Zaira Salvador
B.Sc., M.Sc.
Bachelor's Degree in Biotechnology from the Technical University of Valencia (UPV). Biotechnology Degree from the National University of Ireland en Galway (NUIG) and embryologist specializing in Assisted Reproduction, with a Master's Degree in Biotechnology of Human Reproduction from the University of Valencia (UV) and the Valencian Infertility Institute (IVI) More information about Zaira Salvador
License: 3185-CV
Adapted into english by:
 Sandra Fernández
Sandra Fernández
B.A., M.A.
Fertility Counselor
Bachelor of Arts in Translation and Interpreting (English, Spanish, Catalan, German) from the University of Valencia (UV) and Heriot-Watt University, Riccarton Campus (Edinburgh, UK). Postgraduate Course in Legal Translation from the University of Valencia. Specialist in Medical Translation, with several years of experience in the field of Assisted Reproduction. More information about Sandra Fernández

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