Dalziel Stuart R, Fenwick Sheryl, Cundy Tim, Parag Varsha, Beck Thomas J, Rodgers Anthony, Harding Jane E
Clinical Trials Research Unit, University of Auckland, Auckland, New Zealand.
J Bone Miner Res. 2006 Aug;21(8):1175-86. doi: 10.1359/jbmr.060516.
Small birth size is associated with reduced adult bone mass. We determined if antenatal betamethasone exposure, birth weight, or prematurity affects peak bone mass in 174 adults. Antenatal betamethasone exposure did not. Lower birth weight and prematurity predicted reduced adult height. Slower fetal growth rather than prematurity predicted lower bone mass, but this lower bone mass was appropriate for reduced adult height.
Small size at birth is reported to be associated with lower bone mass in adulthood. However, previous studies have not distinguished the relative contributions of length of gestation and fetal growth to size at birth. Fetal exposure to excess glucocorticoids has been proposed as a core mechanism underlying the associations between birth size and later disease risk. Antenatal glucocorticoids are given to pregnant women at risk for preterm delivery for the prevention of neonatal respiratory distress syndrome in their infants. We determined the relationship of antenatal exposure to betamethasone, birth weight, and prematurity to peak bone mass and femoral geometry in the adult survivors of the first randomized trial of antenatal glucocorticoids.
We studied 174 young adults (mean age, 31 years) whose mothers participated in a randomized trial of antenatal betamethasone. Mothers received two doses of intramuscular betamethasone or placebo 24 h apart. Two thirds of participants were born preterm (<37 weeks gestation). We measured indices of bone mass and size and derived estimates of volumetric density and bone geometry from DXA assessments of the lumbar spine, femur, and total body.
There were no differences between betamethasone-exposed and placebo-exposed groups in any of the lumbar spine, femur, or total body DXA measures. There was no effect of antenatal betamethasone on adult height, although leg length was increased relative to trunk length (p = 0.002). A lighter birth weight (p <or = 0.001) and lower gestational age (p = 0.013) were associated with shorter stature (height Z scores) at age 31 years. Prematurity had no effect on peak bone mass or femoral geometry. However, lower birth weight, independent of gestational age, was associated with lower later bone mass (p < 0.001 for lumbar spine and total body, p = 0.003 for femoral neck BMC). These effects on bone mass were related to bone size and not to estimates of volumetric density. In the femur, lower birth weight, independent of gestational age, was associated with narrowing of the upper shaft and narrow neck regions.
Antenatal betamethasone exposure does not affect peak bone mass or femoral geometry in adulthood. Birth weight and prematurity predict adult height, but it is slower fetal growth, rather than prematurity, that predicts lower peak bone mass. The lower peak bone mass in those born small is appropriate for their adult height.
出生时体型小与成人骨量减少有关。我们确定了产前倍他米松暴露、出生体重或早产是否会影响174名成年人的峰值骨量。产前倍他米松暴露并未产生影响。较低的出生体重和早产预示着成人身高降低。胎儿生长缓慢而非早产预示着骨量较低，但这种较低的骨量与成人身高降低相适应。
据报道，出生时体型小与成年后骨量较低有关。然而，先前的研究并未区分妊娠期长度和胎儿生长对出生时体型的相对贡献。胎儿暴露于过量糖皮质激素被认为是出生时体型与后期疾病风险之间关联的核心机制。产前给予有早产风险的孕妇糖皮质激素以预防其婴儿的新生儿呼吸窘迫综合征。我们在第一项产前糖皮质激素随机试验的成年幸存者中确定了产前倍他米松暴露、出生体重和早产与峰值骨量及股骨几何形态的关系。
我们研究了174名年轻成年人（平均年龄31岁），他们的母亲参与了一项产前倍他米松随机试验。母亲们接受了两剂间隔24小时的肌肉注射倍他米松或安慰剂。三分之二的参与者为早产（妊娠<37周）。我们测量了骨量和尺寸指标，并通过腰椎、股骨和全身的双能X线吸收法（DXA）评估得出体积密度和骨几何形态的估计值。
在腰椎、股骨或全身的任何DXA测量中，倍他米松暴露组和安慰剂暴露组之间均无差异。产前倍他米松对成人身高没有影响，尽管腿长相对于躯干长度有所增加（p = 0.002）。较轻的出生体重（p≤0.001）和较低的孕周（p = 0.013）与31岁时较矮的身材（身高Z评分）相关。早产对峰值骨量或股骨几何形态没有影响。然而，独立于孕周的较低出生体重与后期较低的骨量相关（腰椎和全身p < 0.001，股骨颈骨矿物质含量p = 0.003）。这些对骨量的影响与骨大小有关，而与体积密度估计值无关。在股骨中，独立于孕周的较低出生体重与股骨干上部和颈部狭窄区域变窄有关。
产前倍他米松暴露不会影响成年后的峰值骨量或股骨几何形态。出生体重和早产预示着成人身高，但预测较低峰值骨量的是胎儿生长缓慢，而非早产。出生时体型小的人较低的峰值骨量与他们的成人身高相适应。
