The Impact of Maternal Age and Ovarian Age on Fertility
By Steven D. Spandorfer, MD

INTRODUCTION

     Age is the most important single variable influencing outcome in assisted reproduction.  The effect of advancing age on clinical infertility is manifested not only in the pattern of ovarian response to superovulation, but also in reduced implantation efficiency and an increased spontaneous abortion rate. In this article, we will explore the physiologic mechanisms behind this reduced implantation efficiency and its effect on infertility outcomes.

EPIDEMILOGY OF INFERTILITY

            Infertility is evolving.  As the overall health and wealth of the United States has improved there has been a dramatic decrease in the birth rate.  One of the prevailing theories to explain this phenomenon has been that women are more often entering the work force, thereby delaying marriage and childbearing.  The modern development of oral contraception has allowed the working woman to delay her childbearing and therefore, the impact of maternal aging on fertility has become an increasingly important issue.  Attempting pregnancy at 40 is far different than that at 25 years of age.  Fecundability (ability to conceive) decreases and the spontaneous miscarriage rate increases with increasing maternal age.  Therefore, advancing maternal age has become a very important issue for modern fertility.

MATERNAL AGE, REDUCED FERTILITY AND OVARIAN RESERVE  

     A physiologic decrease in fecundity as maternal age increases has been observed.  In the 1950’s, a comprehensive analysis of the fertility rates of the Hutterite sect of the western United States and Canada was undertaken1. This sect originated in Switzerland in 1528, and practically all of the living Hutterites came to South Dakota in the 1870’s.  Because contraception is prohibited and the communal nature of this sect removes economic burdens, there is no incentive to limit the size of families.  Furthermore, sexually transmitted diseases were almost non-existent.  As a result, the birth rate of the Hutterites is one of the highest on record, with an average of 11 live births per married woman.  Only 5 of 209 women studied had no children, for an infertility rate of 2.4%.  There was a definite decrease in fertility with advancing age; 11% of women bore no children after the age of 34, 33% of women had no children after the age of 40, and 87% of women were infertile by the age of 45.  The average age of the last pregnancy was 40.9 years.  This analysis highlights the enormous decline in fecundity after the age of 40 years.

     Although there is an apparent decrease in the frequency of sexual intercourse with advancing age, this does not fully account for the decline in female fertility.  A French study of couples treated with donor insemination for isolated male factor infertility, has revealed that the per cycle pregnancy rate declines with advancing age2.  The cumulative pregnancy rate for women under 30 was 73% after 12 insemination cycles.  In women between the ages of 31 and 35, the cumulative pregnancy rate was 62% over the same time period, whereas women ages 36 to 40 had achieved only a 54% cumulative pregnancy rate.  Therefore, a measurable decline in female fecundity appears to occur at least 15 years before the climacteric.  This decline is independent of frequency of sexual intercourse and is most dependent on maternal age.

     Why does this age-dependent decline in female fertility occur?  Unlike their male partners, women are endowed with a finite and nonreplenishable complement of germ cells.  The maximum number of germ cells actually occurs at midgestation during fetal life, at which time a total of 6-7 million oogonia are present.  Thereafter, the germ cell content irretrievably decreases and no further de novo gametogenesis occurs. Apoptosis and degeneration occur continuously decreasing the total oocyte number.  By birth, a woman is thought to only have 1/6 of her initial oocyte complement (1 million oocytes).  At the onset of puberty, the germ cell mass has already been reduced to approximately 300,000 oogonia.  In other words, before a woman has sufficiently matured physiologically where she can utilize her oocytes, she has already lost almost 95% of her initial complement of gametes.  Thereafter, during the reproductive years, a number of oocytes are stimulated each month with only one or a few becoming dominant while the others undergo atresia.  The absolute number of oocytes therefore continues to diminish with age. 

            At the age of 37 to 38, there is usually an acceleration of follicular loss.  This occurs when the number of follicles reaches approximately 25,0003.  This accelerated loss correlates with a subtle increase in serum follicle-stimulating hormone (FSH) concentration and a decrease in inhibin production.  These hormonal measurements during the early follicular phase of a menstrual cycle (usually on cycle day 3) have allowed clinicains to estimate a woman’s “ovarian reserve”.   The functional capacity of the remaining follicles and germ cells has been termed the “ovarian reserve”, or ovarian age.  The functional ovarian age may be discordant with chronologic age, when accelerated follicular loss and/or diminished functional capacity of the remaining follicles occurs at an earlier age than expected.  The subtle changes, which indicate diminished ovarian reserve, are associated with a markedly reduced fertility potential, often without apparent changes in clinically identifiable characteristics or major alterations in menstrual cyclicity.  In other words, while in a population based study, measurable changes of a rising FSH and a falling Inhibin level occur around age 37 years, for the individual this can occur many years earlier.  Importantly, no clinical characteristics absolutely suggest the presence of this phenomenon of a “poor ovarian reserve” despite a relative youthful age.

AGE AND IVF OUTCOME

     Older women have a poorer prognosis for success after IVF.  An analysis of our results at The Center for Reproductive Medicine and Infertility of The New York Hospital-Cornell Medical Center has revealed that the mean peak estradiol (E2) level on the day of human chorionic gonadotropin (hCG) declines steadily with advancing age.  This decline in the serum E2 concentration is paralleled with a concomitant decrease in the mean number of oocytes retrieved per cycle.  The delivery rate per embryo transfer procedure in our series drops from around 60% in women 30 years of age or younger to 5.2% for women 44 years of age or older. 

            An examination of the embryo implantation rate (as assessed by the presence of a fetal heart beat per embryo transferred) reveals a decline from 33.5% in women under 34 years to 5.9% in women at age 44.  Thus, a single given embryos has only a 16% chance of implanting when from a woman of 44 years of age as compared to her younger counterpart under the age of 34 years.

            We have analyzed 1621 consecutive cycles of IVF for implantation efficiency as a function of age (June 1995 – October 1996).  In this study we found an overall implantation rate of 23.3%.  Table 1 demonstrates the implantation and delivery rates per embryo transfer throughout this study period.  Implantation was noted to remain almost constant until the age of 35, and then decreased in a significant linear fashion by approximately 2.77% per year (R2 = 0.975; p < 0.0001).  Even when analyzing the sub-group of women with pure male infertility and no identifiable female factor, this same response of diminished implantation efficiency with advancing maternal age was noted.

OOCYTE DONATION AS A MODEL OF IMPLANTATION EFFECIENCY

            Oocyte donation serves as a useful in vivo model to further understand the impaired implantation efficiency seen in older women.  Several authors have suggested that the successful implementation of oocyte donation in women older than 40 years suggests that the endometrium of older women retains normal receptivity.7,8 One investigative team failed to show a decrease in the implantation rate per transferred embryo in women older than 40 years undergoing donor oocyte transfer compared to younger recipients9. In a subsequent report, pregnancy outcomes in younger IVF donors were compared with those in their respective older recipients who shared oocytes from the same cohort10.  There was no statistically significant difference in clinical pregnancy and delivery rates between the donors (33% and 23%, respectively) and recipients (40% and 30%, respectively).  These data suggest that oocyte quality, rather than uterine factors, is the primary determinant of human implantation efficiency.

     However, other investigators have suggested that uterine factors may also play a role in the age-related decline in fecundity.  It has been reported that there may be a slight reduction in the embryo implantation rate in women older than 40 years undergoing oocyte donation, which can be offset by doubling the dosage of exogenous progesterone11.  We have also examined the issue of implantation efficiency in older women at our donor oocyte program.  Twenty-four IVF patients who donated half of their oocytes were studied along with their respective recipients. The mean age of donors and recipients was 32.3 and 40.0 years, respectively.  Although the ongoing pregnancy rate for donors (62.5%) and recipients (58.3%) was similar, there was a statistically significant decrease in the per embryo implantation rate in the recipients (25.6%) compared with the donors (42.5%).  These data taken together suggest that there is a subtle decrease in implantation efficiency in older donor oocyte recipients, which may be overcome by performing multiple embryo transfers or by manipulating the hormonal milieu.  Thus, although oocyte quality appears to be the major factor associated with the reduction in fecundity with advancing age, uterine factors and reduced endometrial receptivity may also play a role.

MATERNAL AGING AND SPONTANEOUS MISCARRIAGES

            Maternal age is also a significant factor in determining the miscarriage rate in after successful implantation (as defined as a positive fetal heart).  We have reviewed 2346 consecutive IVF clinical pregnancies (1991-95) and analyzed the pregnancy loss rate by maternal age. The overall pregnancy loss rate after demonstrating a FH during a 7 week U/S was 11.31%.  A highly significant trend demonstrated an increase in fetal loss when comparing the four age groups ( < 30 yrs = 4.95% vs. 31-34 yrs = 9.46% vs. 35-39 yrs = 11.57 % vs. > 40 yrs = 21.28%; P < 0.0001). 91.3% of the losses in women over the age of 40 were chromosomally abnormal as compared to 71.1% of the losses in women under the age of 40 years. Thus, there exists a highly significant increase in pregnancy loss after demonstrating a FH during a 7 week U/S with increasing maternal age. The overwhelming explanation for these losses appears to be chromosomal in nature with almost 80% having an abnormal chromosomal composition.

OVARIAN RESERVE

            Determining basal FSH and E2 concentrations early in the follicular phase can assess ovarian reserve.  Serum FSH concentrations in the early follicular phase appear to rise several years before the menopause.  It is hypothesized that elevated levels of FSH may result from the reduced secretion of inhibin from the germ-cell depleted ovaries.  These subtle elevations, signaling a decline in the ovarian reserve even in women with regular menstrual cycles, have been typically associated with poor responses to gonadotropin stimulation.  An elevated FSH concentration of greater than 20 mIU/Ml (the ansolute number of FSH elevation depends on the assay utilized and should be individualized by lab) on day 3 of the menstrual cycle has predicted a markedly diminished chance for success after IVF and related assisted reproductive therapies.(12,13)  We have recently demonstrated that elevated E2 levels in the early follicular phase also represent a poor prognostic sign for IVF outcome.  There were very few successful pregnancies in women with elevated E2 levels (>75 pg/mL) on day 3 of the menstrual cycle.  It is theorized that elevated FSH concentrations in the late luteal phase of the preceding cycle may cause latter aberration.

     We have further examined the relationship between basal day 3 hormonal values and IVF outcome.  An analysis of 1249 gonadotropin-stimulated cycles in 782 women treated at Cornell without gonadotropin-releasing hormone agonist (GnRHa) down-regulation, where basal day 3 FSH and E2 were determined concomitantly in the cycle of stimulation, reveals that both influence IVF outcome14.  The ongoing pregnancy rate per retrieval in this series in women with day 3 FSH levels of >20 mIU/mL was one-half of that in women with day 3 FSH concentration <10 mIU/mL.  The same was true for the embryo implantation rate as well.  In this series, the ongoing pregnancy rate per retrieval fell by more than one-half when the day 3 E2 was >75 pg/mL  as compared to when the E2 level was <30 pg/mL. Women with a high basal E2 level rarely exhibit a concomitant elevation in FSH, due to feedback inhibition.  In short, meaningful interpretation of basal hormonal values in the assessment of ovarian reserve requires the simultaneous determination of FSH and E2 on day 3 of the menstrual cycle.  Both have been shown to impact IVF outcome as measured by pregnancy rates and embryo implantation rates. Low early follicular phase inhibin-B concentrations may complement FSH and E2 as markers of ovarian reserve.  As this assay becomes more clinically available, it too can be added as a prognostic assessment of a woman’s “ovarian reserve”.  Finally, a number of provocative tests have been devised to assess ovarian reserve indirectly.  The clomiphene challenge test and the early E2 response to leuprolide acetate administered during a flare protocol have both been reported to be useful tests of ovarian reserve. 

SUMMARY

      Advanced maternal age is associated with a decrease in fecundity potential.  Diminutions in implantation and pregnancy rates are generally seen after the age of 35, and diminish significantly after the age of 40.  Oocyte factors are felt to be primarily responsible; however, uterine factors may also play a role.  Hormonal assessments of FSH and E2 levels on day 3 of the menstrual cycle are reliable measures of diminished ovarian reserve and the anticipated response to ovulation induction.  A similar decrease in implantation rates and pregnancy rates are seen in older women undergoing assisted reproductive techniques, including IVF.  The decrease in implantation efficiency seen in older women undergoing IVF appears to be independent of the magnitude of stimulation response.  Maternal aging appears to be the single most important factor in predicting fertility outcome.

Steven Spandorfer, M.D. can be reached at The Center for Reproductive Medicine and Infertility, The New York Presbyterian Hospital – Cornell University Medical Center, New York, New York

Phone: (212)746-1762

Email: IVF@nyp.org

Website: http://www.ivf.org

REFERENCES    

1.         Tietze C:  Reproductive span and rate of reproduction among Hutterite women.  Fertil Steril 1957; 8:89-97.

2.         Federation CECOS, Schwartz D, Mayaux JM:  Female fecundity as a function of age: results of artificial insemination in 2193 nulliparous women with azoospermic husbands.  New Engl J Med 1982; 306:404-406.

3.                  Faddy MJ, Gosden RG, Gougeon A, Richardson SJ, Nelson JF: Accelerated disappearance of ovarian follicles in midlife: implications for forecasting menopause.  Hum Reprod 1992; 7:1342-1346.

4.     Munne S, Alikani M, Tomkin G, Grifo J. Embryo morphology,developmental rates and maternal age are correlated with chromosomal abnormalities. Fertil Steril 1995; 64:382-91. 

5.         Lim AST, Tsakok MFH. Age related decline in fertility: a link to degenerative oocytes? Fertil Steril 1997; 68:265-71. 

6.         Fujino,Y, Ozaki K, Yamamasu S, et al. DNA fragmentation of oocytes in aged mice. Hum Reprod 1996; 11:1480-83. 

7.         Sauer MV, Paulson RJ, Lobo RA:  Reversing the natural decline in human fertility. An extended clinical trial of oocyte donation to women of advanced reproductive age.  J Am Med Assoc 1992; 268:1275-1279.

8.         Antinori S, Versaci C, Gholami GH, Panci C, Caffa B: Oocyte donation in menopausal women. Hum Reprod 1993; 8:1487-1490.

9.         Sauer MV, Paulson RJ, Lobo RA:  Preliminary report on oocyte donation extending reproductive potential to women over 40.  N Engl J Med 1990; 323:1157-1160.

10.       Navot D, Bergh PA, Williams MA, Garrisi GJ, Guzman I, Sandler B, Grunfeld L: Poor oocyte quality rather than implantation failure as a cause of age-related decline in female fertility.  Lancet 1991; 337:1375-1377.

11.       Meldrum DR: Female reproductive aging-ovarian and uterine factors.  Fertil Steril 1993; 9: 1-5.

12.       Muasher SJ, Oehninger S, Simonetti S, Matta J, Ellis LM, Liu H-C, Jones GS, Rosenwaks Z: The value of basal and/or stimulated serum gonadotropin levels in prediction of stimulation response and in vitro fertilization outcome.  Fertil Steril 1988; 50:298-307.

13.       Toner JP, Philput C, Jones GS, Muasher SJ: Basal follicle stimulating hormone (FSH) level is a better predictor of in vitro fertilization (IVF) performance than age.  Fertil Steril 1991; 55:784-791.

14.       Licciardi FL, Liu H-C, Rosenwaks Z:  Day 3 estradiol serum concentrations as prognosticators of stimulation response and pregnancy outcome in patients undergoing in vitro fertilization.  Fertil Steril 1995; 64:991-994.

15.     Cohen J, Alikani M, Trowbridge J, Rosenwaks Z. Implantation efficiency by selective assissted hatching using zona drilling of human embryos with poor prognosis.  Hum Reprod 1992; 7:685-91.

 

Age	Number	Implantation Rate (%)	Delivery/ Transfer (%)
< 25	28	24.4	50.0
26	13	28.9	53.8
27	20	32.7	65.0
28	28	37.5	50.0
29	48	31.9	62.5
30	57	35.4	57.9
31	89	33.0	60.7
32	69	33.0	52.2
33	92	36.8	65.2
34	113	29.5	54.0
35	133	31.0	51.1
36	125	28.2	44.8
37	138	23.8	49.3
38	150	18.9	40.0
39	121	18.8	38.8
40	108	16.3	36.8
41	111	14.0	29.7
42	77	9.9	22.1
43	71	5.1	15.5
44	19	5.9	5.8
>44 44	11	2.3	0