Risk Factors in Pregnancy that may predispose to Disabilities

Summary: During the first 3 months of pregnancy, many drugs, chemicals, infections, trauma and radiations may alter the fetal genetic make-up to cause abnormal babies. Later stages of pregnancy are only relatively but not completely safe regarding development of genetic defects. These defects include Cerebral Palsy, Mental Retardation and Autism.

CONTENTS

Last updated 10th March 2015 		Ferus at end of each trimester

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General Disabilities

In a large prospective study [Antecedents of cerebral palsy. I. Univariate analysis of risks., by Nelson KB and Ellenberg JH, Am J Dis Child, 1985 Oct, 139:10, 1031-8 ], risk factors in pregnancy that may cause CP was evaluated. This study observed a relatively large increases in the CP rate in association with :

  • seizure disorders
  • maternal mental retardation
  • hyperthyroidism
  • administration of thyroid hormone and estrogen in pregnancy

Some risk factors were predictive of CP only in so far as they were associated with

  1. low birth weight
  2. low Apgar scores

Among factors not significantly related to CP rate were

  • maternal age
  • socioeconomic status
  • smoking history
  • moderate hypertension
  • maternal diabetes
  • use of oxytoxics for initiation or augmentation of labor
  • use of anesthetic agents
  • kidney or bladder infection
  • long cord
  • first trimester (first three months of pregnancy) vaginal bleeding
  • number of children
  

Factors which were not shown to be a risk factor were

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Cerebral Palsy

According to a case-control study [Case-control study of antenatal and intrapartum risk factors for cerebral palsy in very preterm singleton babies., Murphy DJ et al, Lancet, 1995 Dec 2, 346:8988, 1449-54] , carried out on 59 very preterm babies who developed cerebral palsy, identified from a population-based register, and 234 randomly selected controls, the researchers found that :

  • The frequency of cerebral palsy decreased with increasing gestational age and birthweight
  • Antenatal complications occurred in 215 (73%) of the women with preterm deliveries
  • Pre-eclampsia was associated with a reduced risk of cerebral palsy (0.4 [0.2-0.9]), as was delivery without labour (0.3 [0.2-0.7]).
  • There was no increased risk of cerebral palsy with intrauterine growth retardation (1.0 [0.9-1.1]).
  • Factors associated with an increased risk of cerebral palsy after adjustment for gestational age were :
    1. chorioamnionitis (odds ratio 4.2 [95% CI 1.4-12.0])
    2. prolonged rupture of membranes (2.3 [1.2-4.2])
    3. maternal infection (2.3 [1.2-4..5])

The authors concluded that the effect of rigorous management of adverse antenatal factors on the frequency of cerebral palsy in very preterm babies should be tested in randomised controlled trials.

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Cerebral Palsy : Other factors

The relative risk of developing brain lesions predictive of CP during exposure to maternal infection and exposure to placental infection was studied [Maternal infection and cerebral palsy in infants of normal birth weight, Grether and Nelson, JAMA, 1997 Jul 16, 278:3, 207-11]. It was seen that there was an increased risk of CP with :

Among children with CP, those born to infected women were more often hypotensive, needed intubation, had neonatal seizures, and received a clinical diagnosis of hypoxic-ischemic encephalopathy.

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Multiple Risk factor statistics

The role of one or more maternal risk factors,was studied to asses relative risk levels [Antenatal and perinatal conditions correlated to handicap among 4-year-old children., Holst K; Andersen E; Philip J; Henningsen I, Am J Perinatol, 1989 Apr, 6:2, 258-67] among a birth cohort of 4102 mothers and 4138 children. Out of 4038 children (twins and neonatal deaths were excluded), 44 had handicaps like cerebral palsy, mental retardation [mild and severe], epilepsy, severe defects of vision and hearing.

  • Eleven percent of all mothers had three or more risk factors and they had 43% of the handicapped children.
  • Premature rupture of membranes for more than 24 hours was also significantly associated with later handicaps.
  • A combination of three or more maternal risk factors was found to be a predictor of risk for children with later handicaps, with an incidence 11 times higher than in mothers with no risk factors.
  • Of complications at delivery, asphyxia during birth, as evident from Apgar scores of less than 7 at 1 minute and less than 10 at 10 minutes in particular, was a strong predictor of a later handicap.
  • Multiparity increased the risk in all risk categories.
  • The perinatal complication most strongly associated with later handicaps was low birthweight. Forty-eight percent of the affected children had a birthweight of less than 2500 gm and were small for gestational age.

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Placental Defects causing disabilities

Many newborns who appear normal at birth later manifest substantial neurologic and other disease. Placental pathology frequently reveals the cause of cerebral palsy, mental retardation, and other neurodevelopmental disorders [Some placental considerations related to neurodevelopmental and other disorders, Altshuler G, J Child Neurol, 1993 Jan, 8:1, 78-94]. Pathologists are able to explain some of that sad enigma. These studies require examination of placenta for gross and light microscopic placental abnormalities :

  • Chorioamnionitis is now proven to be the major cause of premature onset of labor and prematurity.
  • Ascending bacterial intrauterine infections may cause placental and umbilical vasocontraction leading to fetal hypoperfusion.
  • The fetus may have taken in a lot of meconium while inside the mother, particularly so when the fetus is postmature. This may go un-noticed if the event occurred 4 days or more prior to delivery. Intra-amniotic meconium associated with oligohydramnios (low volume of intrauterine fluid) probably causes placental and umbilical vasocontraction. Meconium probably thus contributes to the vasoconstriction of lung, persistent fetal circulation, necrotizing enterocolitis, and damage of the fetal brain, liver, and kidneys.

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Rehabilitation of brain disabilities in infancy

Studies into the brain [Problem of rehabilitation in perinatal lesions of the central nervous system, Semenova KA, Vestn Akad Med Nauk SSSR, 1990, :8, 21-6] of fetuses, newborns, and infants with a history of infection or intoxication during pregnancy suggest a possibility for development of viral, bacterial, and fungal brain infections inside the uterus. These conditions may resolve after birth or persist for a number of years thereafter, and may induce an immune reaction directed towarsd ones own tissues, causing the birth defects referred to. Rehabilitation of such cases may require drugs to modify immunity. Besides massage and exercise, a new method of local hypothermia has found wide application in various types of dysarthrosis in children with cerebral palsy.

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