Comparing neonatal outcomes with assisted reproduction versus spontaneous conception

This study investigated neonatal outcomes (NOs) after embryo transfer (ET) compared to spontaneous conception (SC). 

They found that fresh and frozen ETs were associated with some adverse NOs such as preterm birth (PTB). 

Assisted reproductive technology (ART) is used to treat infertility. Infertility rates are increasing and so ART is relied on more commonly. ART includes procedures like in vitro fertilisation (IVF). This involves fertilizing eggs in a lab. After IVF embryos can be transferred to the uterus immediately. This is called a fresh embryo transfer (FrET). They can also be frozen and transferred at a later stage. This is called a frozen embryo transfer (FzET). Both methods of ET have been successful in achieving live birth. 

ART pregnancies are at a higher risk of adverse neonatal outcomes (NOs). These include low birth weight (LBW) and small for gestational age (SGA). It is unclear if the type of ET increases the risk of adverse NOs compared to spontaneous conception (SC).

This study analyzed 14 other studies on NOs after ART. The authors compared NOs between FzET and FrET. These were then compared to NOs in SC pregnancies. NOs included LBW, SGA, preterm birth (PTB), and large-for-gestational-age (LGA).

The risk of PTB was 64% greater with FrET and 39% greater with FzET, respectively. FrET was associated with a 67% higher risk for LBW and a 46% higher of SGA. FzET was not associated with a significant risk of LBW or SGA compared to SC. FzET was associated, however, with a 57% higher risk of LGA.

The authors concluded that fresh and frozen ET were associated with some adverse NOs compared to SC.

This study did not take into account some factors. One of these was the cause of infertility. This could have an effect on NOs. More controlled studies are needed.