Letters

Maternal age and fetal loss

Missing abortion stratification adds to confusion

Having an induced abortion increases risk in future pregnancies

Data should have been stratified for smoking habit

Older women have increased risk of unexplained fetal deaths

Risks of having children in later life need to be explained

Missing abortion stratification adds to confusion

EDITORThe objective of Nybo Andersen et al's study of fetal loss was to measure the age related risk of fetal loss "taking into account a woman's reproductive history."¹ To this end the authors stratified the women according to parity and previous spontaneous abortions but inexplicably omitted stratification by induced abortions. Their only reported use of their complete data on induced abortions was to deduct from the count of fetal loss any miscarriages that occurred before an intended abortion.

The effect of elective abortion on future reproductive health is contentious. Some investigators have found statistical associations between induced abortion and subsequent miscarriages and ectopic pregnancies.² Others have reported that there is no significant association between abortion and either of these events.³ Colleagues of the authors at the Danish Epidemiology Science Centre, using many of the same data, have recently reported a strong association between induced abortion and subsequent preterm and post-term deliveries, a finding that adds to concerns that induced abortion may degrade reproductive health.⁴

Numerous studies have shown that abortion is closely associated with other confounding factors, such as smoking, alcohol, and drug use; promiscuity; and venereal disease (citations to several of these studies are included in my rapid response to Nybo Andersen et al's study on bmj.com⁵). These behaviours may help women to cope with unresolved anxiety and depression after abortion. Women with a history of abortion are especially likely to persist in using tobacco, alcohol, and illegal drugs during subsequent pregnancies.⁵ This may be because the subsequent wanted pregnancy is a connector to unresolved issues after abortion.

The daunting task of properly sorting out these confounding interactions, incidental associations, and hidden proxy effects has barely begun. Therefore, researchers working with large registry based datasets should always stratify separately for induced abortion. The failure to do so only postpones clarification of important research issues. In Nybo Andersen et al's study the failure to stratify for induced abortion is even more egregious since stratification was done for spontaneous abortion.

Finally, given the political passions associated with induced abortion, researchers should always stratify for itif only to avoid arousing the suspicion that they are suppressing data for ideological reasons.

David C Reardon, director. 
Elliot Institute, PO Box 7348, Springfield, IL 62791, USA dave12{at}famvid.com

Having an induced abortion increases risk in future pregnancies

EDITORThe latest of three Danish reports about reproductive history informs readers that "fetal loss is high in women in their late 30s or older, irrespective of reproductive history. This should be taken into consideration in pregnancy planning and counselling."¹

Consider a woman whose first pregnancy occurs at age 30. According to Melbye et al and Zhou et al, if she is pressured to have an induced abortion she should be warned that if she does so she will increase her risk of never having a birth. ^{2 3} Will the abortion clinic tell her that her best chance for a full term birth is to carry her current pregnancy to term? No, it will not; no abortion clinic's consent form mentions such a risk. Even if the woman does have a future birth, a previous induced abortion roughly doubles the risk that it will be very preterm (less than 34 weeks' gestation), according to another study of Danish women (relative risk 1.99 (95% confidence interval 1.64 to 2.43)).³ If the woman has two evacuation-type abortions she increases her risk of preterm birth by 1155% (5.14 to 30.64).³ There are at least nine other reports that found an increased risk of prematurity from previous induced abortions ^{4 5} (readers can visit www.vcn.bc.ca/~whatsup for references to 10 studies known to me).

By not informing prospective patients of health risks associated with induced abortion, abortion doctors are violating their legal duty to protect health and not needlessly endanger it. Is there any serious health risk for a mother who has a preterm birth? In their study of Danish women Melbye et al inform us that if the gestation of a newborn infant is under 32 weeks the mother has doubled her risk of breast cancer compared with having a full term birth (relative risk 2.08 (1.20 to 3.60) for gestation of 29-31 weeks).²

Let us ensure that women of reproductive age are fully informed about health risks of medical treatments to them and their future children.

Brent Rooney, independent medical researcher. 
Reduce Preterm Risk Coalition, 3456 Dunbar St (146), Vancouver, Canada V6S 2C2 stopcancer{at}yahoo.com

Data should have been stratified for smoking habit

EDITORDanish women have a shorter life expectancy than other Nordic women, and one reason for this is probably that Danish women more often smoke. It would have been interesting to see the data in Nybo Andersen et al's paper stratified for smoking habits, as one would expect this to have a strong influence on fetal loss.¹

Mats Reimer, community paediatrician. 
Child Clinic, Molnlycke S-43105, Sweden reimer{at}telia.com

Older women have increased risk of unexplained fetal deaths

EDITORNybo Andersen et al report a comprehensive analysis of the effects of maternal age on the rate of fetal loss.¹ Colleagues and I found that the causes of fetal death (fetuses 500 g) for women of advanced maternal age have changed significantly over the past 30 years.² In a large dataset in Canada, in a study during 1961-74, we found that women aged 35 had a 1.5-fold (95% confidence interval 1.2 to 2.2) increased risk of experiencing a fetal death compared with younger women. This was largely due to an increased risk of lethal congenital anomalies (odds ratio 3.2 (1.6 to 6.5)).

In a study during a later period (1978-95) we found that although the absolute rate of fetal deaths had decreased in all women, the risk decreased less for older women (odds ratio 1.8 (1.4 to 2.6)). It seemed that older women were no longer experiencing an increased risk of fetal losses due to lethal anomalies (odds ratio 0.2 (0.03 to 1.5)). Presumably this is because older women were being screened for anomalies in the first and second trimesters and abortions were readily available.

Interestingly, we found that women aged 35 had an increased risk of unexplained fetal deaths (odds ratio 2.2 (1.3 to 3.8)). These were fetal deaths that occurred in women without any known fetal or maternal risk factors (no maternal history of hypertension, diabetes, abruptio placentae, infection, antepartum bleeding, fetal intrauterine growth retardation, or infection). Like Yudkin et al we found that these fetal deaths occurred late in pregnancy, with two thirds occurring after 35 completed weeks.³ In addition to advanced maternal age, we found that first birth and obesity were significant predictors of this type of loss.⁴

With this information, not only are we better able to counsel our older patients but we can also screen women at risk late in pregnancy in an attempt to reduce these late fetal deaths.

Ruth C Fretts, assistant professor. 
Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA 02214, USA rfretts@caregroup.harvard.ed

Risks of having children in later life need to be explained

EDITORIt is a pity that Stein and Susser confined their editorial on the biological disadvantages of having children in later life to matters obstetric.¹ Their claim that such risks as they and Nybo Andersen et al describe² are outweighed by the possibility that children of a late pregnancy do better at school is debatable; other biological risks should also be considered. One such is the fact that the risk of developing breast cancer increases with a woman's age at first full term pregnancy. There is almost a 2.5-fold difference in the risk of breast cancer between women who have their first child before the age of 20 and those who have their first full term pregnancy after the age of 30. ^{3 4}

As possibilities and demands for having children later in life increase, the whole range of risks needs to be explained.

Alan Rodger, director of radiation oncology. 
William Buckland Radiotherapy Centre, The Alfred, Prahran, Victoria 3181, Australia Alan.Rodger{at}med.monash.edu.au