Fetal lethal defects. What does this mean?


Lethal defects are severe developmental disorders that directly or indirectly lead to the death of the foetus or newborn baby. They can be caused by genetic or non-genetic factors. They are characterised by an impaired development of the foetus which results in an inability to carry the pregnancy, or death shortly after birth. What do I need to know about lethal defects?

  • Lethal malformations are defects of the fetus or newborn that cause its death, regardless of the treatment undertaken. In Poland, 1074 terminations of pregnancy due to fetal malformations were carried out in 2019
  • On 22 October, termination of pregnancy due to fetal malformations was declared unconstitutional
  • Among the lethal defects of the fetus, we can distinguish neural tube defects, which lead, among others, to brainlessness and cranium, and chromosome trisomies – Patau’s and Edwards’ syndrome
  • In the majority of cases, treatment of newborns born with lethal defects is abandoned, considering the treatment to be persistent therapy

Every woman who is pregnant or planning to have children should feel safe and receive the best possible medical care. Purchasing a medical package for pregnant women can help.

What are lethal defects?

A lethal defect in a foetus or a newborn baby is a developmental disorder with an uncertain or poor prognosis which leads to spontaneous abortion, premature birth, intrauterine death and, in the case of newborn babies, premature death, regardless of the treatment given. Lethal defects also include those birth defects that do not lead to death shortly after birth, but cause the child to suffer continuously and require palliative care in perinatal hospice. What are lethal defects

Worldwide reports estimate that 3.3 million children under the age of five die each year from major congenital malformations. Until recently, in Poland, the finding of a lethal defect in a foetus was the basis for terminating a pregnancy. On 22 October, the Constitutional Tribunal ruled that termination of pregnancy due to lethal defects in the fetus is unconstitutional, and thus banned de facto legal abortion in Poland. In 2019, 1110 official terminations of pregnancy were carried out in our country, of which 1074 due to a high probability of severe and irreversible fetal impairment or an incurable life-threatening disease.

The diagnosis of a lethal defect is preceded by a number of tests, including ultrasound, echocardiography, genetic or prenatal tests.

Examples of fetal lethal defects:

Among the lethal defects that are diagnosed in the fetus or newborn are:

  • brain malformations – holoprosencephaly, craniosynostosis, cerebral hernias;
  • critical heart defects or absence of heart
  • triploidy
  • trisomy 18 of a pair of chromosomes (Edwards syndrome)
  • trisomy 13 of a pair of chromosomes (Patau syndrome)
  • monosomy of autosomal chromosomes
  • certain bone dysplasias
  • certain genodermatoses
  • Smith, Lemle and Opitz syndrome with holoprosencephaly,
  • metabolic diseases – Krabbe disease or Zellweger syndrome
  • renal agenesis
  • syringomyelia with absence of urinary bladder,
  • complex malformations – Neu-Levox syndrome, lethal polycystic syndrome.

Patau syndrome (trisomy 13) is one of the most rare and severe forms of trisomy found in live-born infants. It occurs with a frequency of 1 in 8-12 thousand births. The risk of this lethal defect in a newborn increases with the age of the mother. In most cases, foetuses with trisomy 13 die in utero or are stillborn. If the newborn is born alive, the average life expectancy is about 3 years. Read more about this lethal defect: Patau syndrome (Patau syndrome) – trisomy of chromosome 13

Examples of fetal lethal defects

Edwards’ syndrome (trisomy 18) occurs once in every 3,500 to 5,000 births. It is a genetic disease which in almost 95 per cent of cases leads to a spontaneous miscarriage in the first trimester of pregnancy. In most cases, live-born infants with this genetic defect live at most for two months, in rare cases, they survive more than a year. See more: Edwards syndrome – trisomy 18 chromosome

In 2019, there were 88 terminations of pregnancy due to a diagnosis of Patau or Edwards syndrome with coexisting somatic defects and 60 terminations without coexisting defects.

Lethal defects also include neural tube defects, which are one of the causes of miscarriage in the first trimester of pregnancy and death of children in the first year of life. Neural tube defects are divided into defects of the brain and skull: cerebral aponeurosis, cranial aponeurosis, cerebral hernias, skull and spina bifida, and defects of the spinal cord and spinal canal: spina bifida, meningomyelocele, spina bifida, hydrocephalus and spinal cord cavernoma.


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