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When Louise Brown was born on 25 July 1978, she kicked off an era. The first "test tube baby" is a mother herself now, and she’s been joined by millions of others born with the {{U}} (47) {{/U}} of in vitro fertilization (体外受精), or IVF. Now specialists wonder whether people who were conceived by IVF are likely to be {{U}} (48) {{/U}}.
"By and large, the kids are just fine. It’s not like the kids having {{U}} (49) {{/U}} arms or heads," says Carmen Sapienza, a scientist at Temple University. But none is older than their early 30s, and the vast {{U}} (50) {{/U}} are under the age of 20, so they haven’t had time for long-term health problems to show up.
One source of worry is that so many IVF babies have low birth weight. Children-conceived through IVF are more likely to {{U}} (51) {{/U}} less than 2.5 kilograms than are babies conceived {{U}} (52) {{/U}}. That could spell trouble ahead, because l

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