MCHB/EPI Miami Conference — December 7 - 9, 2005

Maternal Age: In the Tails of the Distribution

SHAHEEN HOSSAIN: Thank you, Mary. Can everyone hear me okay? All right. Isn't it wonderful that we have the entire room for our self? It's just great, you know. It's almost like a plane, you know, I mean it's like, empty seats, use it for yourself. So, anyhow, I'm very pleased to be here and to have the opportunity to present here. I like to talk about the study we have conducted in Utah to assess the impact of maternal age on fetal death. First, I'd like to acknowledge my co-authors for their contribution in this project, particularly Rob Satterfield, who is sitting right there, for doing all the analysis for this project.

Pregnancy is supposed to be an exciting, right, for new mothers and dad, right? Okay. Because society customizes things for a new pregnant mom. They, you know, parking places, even a phone booth.

Unfortunately, not all pregnancies result in healthy outcomes. It is really unfortunate in 2002 we had more than 25,000 babies who were stillborn in the U.S. And this number is very close to infant deaths. Many people are surprised to know that fetal death rates are happening at this level. The perception is that with the benefits of modern medicine fetal death is extremely rare. However, that's not entirely true. It is true that the fetal death rate has declined significantly over the last few decades, but the rate is still high.

In Utah we did this study for many reasons, like national trend we also found that in Utah fetal death rates and the infant death rates are comparable, yet fetal death rates have received very little attention. In Utah , our fetal death rates are much lower than the nation. However, you can see that it's much higher than the healthy people 2010 goal of 4.1.

Also, we're observing both nationally and locally that women are delaying their childbearing until their 30s and 40s. The U.S. women between 35 to 39 have increased the birthrate by 22 percent. The birthrate among Utah women increased 25 percent, I don't know whether you can see the pointer, during the same age group and during the same time period. So the impact of this trend on fetal mortality is not entirely clear. So we conducted this study to assess the independent e-fact of maternal age on the risk of fetal death. We used eight years of data, we used birth certificate and fetal death data from 1995 to 2002 and we focused on singleton deliveries.

In this slide you can see our main variables. Our outcome variable is fetal death, which is defined as fetal death at 20 or more weeks of gestation. And our independent variable was maternal age and in order to evaluate the impact of age we stratified age into six age groups. And other variables included in our study are also listed here.

We used mostly multi-variant logistic regressions and we used SIDS for our analysis. Our study population included more than 350,000 singleton deliveries and the fetal death rate for the overall period was 4.6.

This slide shows the age of distribution of our study population. As you can see, the younger age group and then the older age group, 35 and plus, accounted more than 18 percent of all births.

This slide shows maternal characteristics by maternal age. I hope you can see the font because some of it's kind of small. If you look at the unmarried status, we find that almost 17 percent of our study population was unmarried. And if you look through the age group, 61 percent of the younger age group they were unmarried, which makes sense. If you look at the nulliparous status, more than one-third was nulliparous, and they started to decline with the advancement in the maternal age, but it is interesting to see that 21 percent of the women between 35 and older are multiporous.

This slide shows the fetal death rate and risk by maternal age and I'm going to talk about the odds ratios. You know, we calculated odds ratio using the logistic regression analysis and we were debating whether to use 20 to 24 or 25 to 29 age group as our referent category, because we did not see much difference between the two groups. So we decided to use 25 to 29 as our referent category. So if you look at the odds ratio we find that it's higher among the younger age group and higher among the older age group, kind of like giving you a U shape. And the risk of fetal death increased with advancing maternal age. Between 30 to 34, women, they have 30 percent increased risk of fetal death. This rate increases to 70 percent among the group 35 to 39. And women 40 and older were three times more likely to experience a fetal death compared to the referent group.

I'm going to go really quick because of the time over this slide. We also explored the marital status, parity and PNC visit, and looked at the impact of each of these on fetal death and found that they all happened to be a risk factor, particularly high parity, which is 4 and more, had 60 percent, women who are high parity have 60 percent more likely to experience a fetal death compared to women who had between 1 and 3 prior live births. And the prenatal care visits, we found that women with no care visits were 8 times more likely to experience a fetal death compared to women who had some visits.

We also explored the maternal complications and pregnancy complications and found that abruptio, women who had this condition were 8 times more likely to experience the fetal death compared to women who did not have this risk factor.

Here you can see the unadjusted odds ratio that we have seen earlier, and we all know about parity, martial status, PNC visit, all have an impact on fetal death. So in our adjusted model we controlled for all those variables. I don't know if you can read this bottom, we controlled for martial status, education, parity, race, ethnicity, congenital anomalies, PNC visits, tobacco use, medical and pregnancy complications, in our model and found that, this is kind of interesting, that the higher odds ratio that we saw in an adjusted model for the younger group did not increase. Rather it dropped, meaning the younger maternal age was not a risk factor for fetal death. However, the rate increased for women 30 to 34 and the women 35 and older retained the higher odds ratio that we have seen in the unadjusted model despite controlling all these confounders. So, this clearly shows that yes, maternal age is a risk factor, but only advanced maternal age.

So why is advanced maternal age a risk factor? And here are some possible explanations provided in the current literature. With age we have more medical conditions, like hypertension, diabetes. With age we have more pregnancy complications, like renal disease or placenta, or placenta (inaudible) It is also more common, the multiple gestation among older women because of the infertility treatment and as you all know the risk of congenital anomalies increases with maternal age, but remember we controlled for all these factors in our regression model. So, the other possible explanation provided in the current literature is that it could be due to the aging of uterine vessels.

This morning you heard from Nancy talking about the impaired vasculatures, so with the aging, particularly when you're older and you're pregnant, it is a lot harder to push the blood flow, meaning that this aging has an impact, you know, in itself.

I have only one more minute so I'll just talk about the limitations of our study that possible underreporting and it's also possible that mother may have other risk factors, like back problem, infection, hemorrhage, that could have really complicated the fetal death rate that we were unable to control. Also, data related to stress, drug use, were not available in the data set, so they could have been the confounding factor and age may have been the marker, but we were unable to control.

So in conclusion, I would say that, yes, advanced maternal age is a risk factor. Women of advanced maternal age need to be informed about this increased risk. We don't want to tell them that advanced maternal age should be an absolute barrier to your reproductive decision. No, they can have children, as long as they understand there is an increased risk. And I would like to mention, you probably have seen it in the New England Journal of Medicine, a recent publication that says childbearing among older women, the message is cautiously optimistic. And again, we need more research to guide our prevention efforts. And thank you for your time.