Page 1 of 1: RADIOGRAPHY OR IONISING RADIATION IN FETAL MATURITY

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Foci of ossification centers have been visualized as early as 14 wks but it is only after 16-18 wks, when fetal skeleton is clearly visualized.
Before that fetal skeleton is insufficiently radio opaque.
Also because of the following risks of ionizing radiations, radiographic investigations are not used esp. in 1st trimester e.g.,
1) Teratogenic Risk
Risk of ionizing radiations is based primarily on the estimated dose and the period of gestation
2) Oncogenic
3) Genetic
4) Fetal death

Exposure of fetus to less than 10 rads is believed to pose little risk to the fetus.
The risks of ionizing radiations are greatest between 6-15 weeks of pregnancy.
However X-rays can be used in late pregnancy in doubtful cases of maturity e.g., for appearance of thickness and density of shadow for ossification centres of fetal skeletal system.
1) If no ossification centres are visible it is possible that the fetus is not at term.
2) Visualization of the ossification centres of the cuboid bone – means that the fetus is at term.
3) If only the lower femoral epiphyses is visualized then the fetus is at 37-37 wks(38 wks)
4) If both the distal femoral and proximal tibial are visualized and well defined then the fetus is at full term 38-40 wks or at least term( 38 wks)
5) If in addition to femoral and tibial, Wrist /Ankle/Sacral centres are seen then pt is beyond full term.
In addition in late pregnancy it can also tell us:
1) Thickness and density of shadow of fetal bones and esp. fetal skull.
2) Overall gross size of the fetal skull and bones
3) Lie and presentation of fetus
4) No of fetuses
5) Absence /presence of H Mole/ IUD/Hydramnios/ gross bony congenital malformations e.g., hydrocephalus/aerocephalus/spina bifida

IMPORTANT: Maternal and fetal ovaries should be protected during the X ray procedure.

NOTE: X rays do not diagnose postmaturity i.e. X ray films for fetal ossification centres usually fail to reveal bony (gest) age of fetus in excess of that expected at full term.

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