Key facts about preterm birth

The World Health Assembly (= decision-making body of WHO) provided the first definition of preterm birth in 1948. Nowadays this is the most extensively used and accepted definition of preterm birth.

The average pregnancy lasts for approximately 37 to 42 weeks. Every baby born before completion of 37 weeks of pregnancy (also called weeks of gestation) is considered as preterm. The following subcategories are used for further distinction:

extremely preterm: <28 weeks of gestation

very preterm: 28 to <32 weeks of gestation

moderate to late preterm: 32 to <37 weeks of gestation

late preterm may still be differed with referring to 34-37 weeks of gestation

Preterm babies are also differentiated in terms of unusually small body length and weight for the number of weeks of pregnancy (gestation period, also called gestational age). Babies born preterm have much higher rates of low birthweight. Low birthweight refers to babies who are born weighing less than 2,500 grams (about 5.51 pounds), very low birthweight to babies with a birth weight less than 1,500 grams (about 3.30 pounds). The concept of small for gestational age describes babies who are smaller than the usual average for the number of weeks of pregnancy.

Worldwide situation

Worldwide, estimated 15 million babies are born preterm annually – that means 1 baby in 10 is born premature. Worldwide. And the number is rising.

Preterm birth complications are the main cause of global under-5 deaths.

Preterm birth complications were responsible for nearly 1 million deaths in 2015.

Three-quarters of them could be saved with current, cost-effective interventions.

Many survivors face a lifetime of disability, including learning disabilities and visual and hearing problems.

Across 184 countries, the rate of preterm birth ranges from 5% to 18% of babies born.

Inequalities in survival rates around the world are stark. In low-income settings, half of the babies born at or below 32 weeks die due to a lack of feasible, cost-effective and basic care, e.g. warmth, breastfeeding support, basic care for infections and breathing difficulties.

In Uganda, the leading causes of neonatal deaths over the past 4 years have been prematurity complications (18%) and septicaemia at 7%. Septicaemia refers to diseases caused by the spread of bacteria and their toxins in the bloodstream of the preterm baby, babies at home a prone to this condition.  15% of the early neonatal deaths had no cause of death documented.

Causes & risk factors

Preterm birth occurs for a variety of reasons. The majority of preterm births happen spontaneously. Experts have identified several factors, which may increase the risk of preterm birth.

Some risk factors are “modifiable,” meaning they can be changed to help reduce the risk, while others cannot be changed. However, in about 50% of cases no cause for the baby born too early can be identified.

Medical conditions

Pregnancy history	For example a mother having born a preterm baby before is at higher risk for another preterm birth within the next pregnancy.
Multiple pregnancy	The most common complication of a multiple pregnancy is preterm birth.
Assisted reproductive technologies	Reproductive treatments are linked to multiple pregnancies and hence to preterm birth.
Uterine or cervical abnormalities	For example, a short cervix might favour preterm birth: during pregnancy, the cervix gradually softens, decreases in length as the baby grows to prepare birth. As consequence the cervix might begin to open too soon.
Infections and chronic conditions	Infections of the uterus (e.g. through urinary tract infections or bacterial vaginosis , an imbalance of the bacteria that are normally present in the vagina) or non-communicable diseases such as for example diabetes, high blood pressure, asthma or renal and cardiac disorders.
Pregnancy complications	Gestational diabetes and pre-eclampsia are two examples of typical pregnancy complications. Due to preeclampsia women may need to give birth early to avoid serious health problems for both, the mother and the baby.
Genetic influece	Specific foetal and maternal genotypes (a person’s type of genes for a particular inheritable trait) are associated with the risk of preterm delivery.

Modifiable lifestyle risk factors

Lifestyle patterns	Factors like an unbalanced diet, underweight or overweight (obesity), smoking, alcohol or drug consumption, a high stress level and exposure to environmental pollutants.
Healthcare	No or late antenatal care might inhibit identification and therapy measures at an early stage.

Demographic factors

Age	Particularly young (< 17) or older women (> 35) are at higher risk for preterm birth.
Sociodemographic determinants	Socioeconomic disadvantages (low education level, low income, few social support) might play a role for preterm birth.
Ethnically	There are higher preterm birth rates reported in black than white women [7, US data].