[Prenatal diagnose of abnormalities of fetal limb bone].

OBJECTIVE

to discuss the prenatal diagnosis of abnormalities of fetal limb bone.

METHODS

we selected 18 cases which long bone of fetus less than 2SD of average volume of gestational weeks or long bone changed into angle or other fetus's abnormalities by first B-mode ultrasonic. All above cases was delivered at Capital Medical University of Obstetric and Gynecological Hospital during Jan. 2006 to Dec. 2009. We B-mode ultrasonic was used to measure fetus's biparietal diameter (BPD), femur length (FL), abdominal circumference (AC), head circumference (HC), humerus length (HL), amniotic fluid index (AFI) and structures of organ and calculated FL/AC, growth speed of long bone. The standard of achondroplasia is that FL and HL are less than 4SD of average of gestational weeks or FL/AC less than 0.16. The standard of Osteogenesis Imperfecta is fetal long bone of fetus shows short and thick, curves into angle, fracture in uterus by X-ray, or skull shows thin or sink by X-ray.

RESULTS

(1) by B-mode ultrasonic and X-ray exam of all 18 cases: 7 cases shows that HC > 2SD, 10 cases shows too much amniotic fluid, 12 cases shows AFI > 18.0, 9 cases shows abnormalities of narrow cavitas thoracis, disordered vertebral column, or unusual architecture of heart. For cases 1 to 14 are achondroplasia, among which, 11 cases are FL < 4SD and HL < 4SD, 2 cases are FL < 3SD and HL < 4SD, 1 case is not only FL < 2SD and HL < 3SD but also hydroncus all over the body of fetus. The growth velocity of long bone of fetus in all the 14 cases is more slowly than the normal rate. For all the above 14 cases, 12 cases FL/AC < 0.16, 1 case FL/AC = 0.19, 1 case FL/AC = 0.20. The length of femur or humerus is shorter than the normal rate and have other abnormalities the above last two cases. For case 15 and 16, they don't show any abnormalities of bone growth though one year's follow up studying. For case 17 and 18, they are osteogenesis imperfecta. (2) The result of fetal perinatal period fate and autopsy: there are 8 female and 10 male in all the 18 cases. One case is labored after 39 weeks pregnancy, and it is low birth weight infant, weight < 3%th. All the other cases are normally birth weight infant. All the 18 cases of abnormalities of fetal limb bone are examined by chromosomes check, among which, 9 cases are amniocentesis, 7 cases are cordocentesis, 2 cases are checked chromosomes by fetus cord blood, all the caryotype are normal. In the 16 autopsy cases, 14 cases are achondroplasia or hypochondroplasis. It can be seen amplifying extremities, hyperplasia chondrocytes of tubiform born, karyomegaly, anachromasis, hyperplasia capillaries though microscope and grow up into cartilage irregularly. Also can be seen hyperplasia chondrocytes of epiphyses, delaying osteosis. 2 cases are osteogenesis imperfecta. It can be seen broadening of metaphyses, exility of bone trabeculae. For the other two cases which the fetus is alive, we do the follow up studying to their one year old one of them is low birth weight new born, their limb and height are all normal.

CONCLUSIONS

to diagnose fetal Achondroplasia, it is not only based on the significantly shorter of femur or humerus length but also based on the dynamics observing the long bone growth velocity and calculating FL/AC. For osteogenesis imperfecta fetus, it should be diagnosed by fractures in uterus though X-ray.