Question of Summer 2003: Is She or Isn’t She?

Not Even Mei Knew for Sure if She Was Pregnant Until There Was No Cub

August 22, 2003 Update:
Mei Xiang's progestins remained at baseline (see final chart). We have concluded that she is not pregnant and she has ended her pseudopregnancy.
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link toHormone profile archive

August 20, 2003 Update:
We received two good quality urine specimens from Mei Xiang on Tuesday afternoon and Wednesday morning. The two most recent values are in the baseline range (8/19, 17ng/mg Cr; 8/20, 18 ng/mg Cr). We consider baseline to be concentrations in the range of 8-29 ng/mg Cr.

August 17, 2003 Update:
Unfortunately, the sample collected today was dilute and of poor quality. The value obtained (13 ng/mg Cr) is therefore unreliable. We will see if better samples can be obtained in the next couple of days to pin down what is going on.

August 16, 2003 Update:
Hormone concentrations still above baseline at 39 ng/mg Cr.

August 15, 2003 Update:
Hormone concentrations are not baseline yet. We were suspicious of the sample collected Thursday because it was overly dilute (10-15 fold more dilute than a typical sample—probably due to water contamination. The two replicates collected today from overnight and mid-morning confirmed that concentrations remain in the range of 30-50 ng/mg Cr. We judge baseline to be 15 ng/mg Cr, or less, and would expect to see concentrations remain at the baseline range for a couple of days, at the least, before we'd be comfortable stating the the pseudopregnancy is concluded. Based on today's values, we have eliminated yesterday's sample from the graph, as it was probably unreliable.

August 14, 2003 Update:
Today's progestin value is in the 'baseline' range, but the sample was quite dilute. Nevertheless, today's value falls very neatly in line with the declining trend. If she were pregnant, Zoo scientist Steve Monfort would have expected to start seeing fairly clear evidence of an uptick in maternal behaviors at this point.

We've yet to see any increased pregnancy behavior from Mei Xiang. She hasn't demonstrated any new nest building since last week and still has not demonstrated cradling or ano-genital licking. She is showingperiods of restlessness in the evenings, as of thelast twp nights, but continues to be very lethargicoverall. No mammary development or significant changes with her vulva either.

August 12, 2003 Update:
Progestins continue to decline to less than 50 ng/mg Cr.

August 11, 2003 Update:
Today's urine sample was very dilute, and this has the effect of making hormonal assessments less accurate. But, taking this into account, the hormone concentration for today appears to support a major decline in progestin excretion. In some pandas (including Bai Yun at the San Diego Zoo), progestin concentrations declined gradually after achieving maxima (during the secondary progestin-rise interval) over about 10 to 14 days. In other cases (including some of Ling Ling's profiles and Mei Xiang's 2002 pseudopregnancy), progestin concentrations tended decline more sharply (but this can vary from year to year) to baseline over about five to seven days.

We are learning new things with every animal we track, but it is safe to say that progestin concentrations are expected to fall to baseline range (<15 ng/mg Cr) before pregnancy or pseudopregnancy ends. In summary, we are most likely very near to the end.

As of Monday morning, we began a 24-hour watch of Mei Xiang. Volunteers are watching for particular behaviors associated with pregnancy and pseudopregnancy, including nest building, object cradling, and ano-genital licking, as well as making other notes. Ano-genital licking appears to be the best indicator of impending birth, and this behavior increases in frequency and duration significantly in the hours preceding birth.

As of today, though, it has been a few days since MX has demonstrated any new nest-building behavior or manipulation of her current nest. Our watch will continue until we have observed at least two days of baseline progesterone metabolite values.

August 10, 2003 Update:
The keepers were unable to collect urine from Mei Xiang on Friday or Saturday, but the value from Sunday shows a sudden drop of about 50 percent from progestin concentrations observed over the past couple of weeks. Keep in mind that what is important is the temporal and qualitative trend. We'll know soon enough if the drop is real once we've had the chance to look a values over the next couple of days.

In the past, the sudden drop in hormone concentrations at the end of pregnancy, or pseudopregnancy, has triggered an increase in the intensity of 'maternal' behaviors (for example, apple cradiling etc.), and this is perhaps related to the 'withdrawal' of hormone stimulation, and a change in the overall hormonal milieu. In any case, keepers are keeping careful note of Mei's behavior.

August 6, 2003 Update:
Still no change; progestin excretion remains quite high.

August 3, 2003 Update:
We couldn't get urine samples from Mei Xiang on July 31 or August 1, but we are seeing continued high progestin excretion. The duration of the secondary progestin rise has been about 50 days, which is a bit longer than we were expecting, but every opportunity to evaluate another pseudopregnancy or pregnancy profile teaches us something new. We will probably be seeing a declining trend in progestins excretion fairly soon.

July 30, 2003 Update:
No change in MX's urinary progestins pattern; concentrations are still in the maximal range. We will update as soon as new data become available.

July 29, 2003 Update:
Urinary progestins continue to be elevated at what appear to be peak concentrations. We'll continue to monitor hormones twice weekly and will provide updates as data become available.

July 25, 2003 Update:
Urinary progestins have increased considerably over the past few days. We will continue monitoring hormone concentrations every two to three days. These concentrations are approaching the 'maximal' levels documented during the 2002 pseudopregnancy. We will be keeping an eye out for a sharp, or consistently downward pattern that might provide an indication that pseudopregnancy has ended, or less likely, that a birth is imminent.

July 22, 2003 Update:
Urinary progestins continue to be elevated above baseline through yesterday, July 21. As one can see from the profile, it is a tricky business to clearly define when the secondary rise began (indicative of pseudopregnancy or fetal development stage), but we are certainly somewhere in the midst of this four-to-six-week stage. A sharp decline in progestin concentrations (5-10 units) will either delineate the end of the pseudopregnancy or coincide with the birth of an offspring.

July 18, 2003 Update:
Mei Xiang's progestin levels remain elevated at about the same concentration and so it appears we still have a few weeks to go until we see the end of pregnancy or pseudopregnancy.

July 11, 2003 Update:
No change to report.

July 8, 2003 Update

Ever since giant pandas Mei Xiang and Tian Tian mated on April 4, everyone at the National Zoo—along with many others in the Washington, D.C., area and around the world—have been waiting anxiously to know whether Mei Xiang became pregnant. Unfortunately, we’ll have to wait a while more.

Diagnosing pregnancy in women is a cinch. A quick test that measures a hormone called human chorionic gonadotropin in urine gives immediate and highly accurate results within about a month of conception. No such luck with giant pandas. In fact, no test, hormonal or otherwise, is yet available to tell whether a female giant panda is pregnant. National Zoo scientists are trying to develop such a test, but that doesn’t help us this year. So, not until a baby panda is born—or not—will we know for sure.

Zoo scientists have been able to track the progress of the panda breeding season through routine hormone analysis. For instance, as described in “Protecting Giant Panda Pregnancy” on April 14, a spike in the levels of estrogen on April 3 indicated that ovulation was imminent and a subsequent increase in urinary progesterone revealed that she had ovulated. And behavior patterns matched those of the hormones. Mei and Tian were showing every sign of being interested in mating on April 3 and did mate on April 4. The mating lasted just 15 seconds, however, leaving Zoo scientists skeptical about the chance that it resulted in fertilization.

It is difficult to diagnose pregnancy in giant pandas because even if mating is unsuccessful, female pandas experience pseudopregnancy. During psuedopregnancy, the female’s hormone profiles and behavior are identical to those she would be exhibiting if she were indeed pregnant. Zoo scientists are still tracking Mei’s hormone levels because they reveal valuable information. For instance, they have been able to identify when the period of embryonic diapause, or its pseudopregnant equivalent, ended. Embryonic diapause, also called delayed implantation, lasts for 30 to 100 days in giant pandas. During this time, the embryo floats freely before finally implanting and commencing fetal development.

During the first weeks of June, about 60 to 70 days after Mei ovulated, scientists witnessed an increasing upward trend in urinary progesterone, which suggests that she was entering into the final four-to-six-week period of either a pseudopregnancy, the most likely outcome, or a true pregnancy. During this period, the progesterone levels will remain elevated. In a pregnancy, this is when the fetus is developing. The very short period of development explains why giant panda cubs are born in such an immature state.

Zoo scientist Steven Monfort explains, "This is Mei’s urinary progestin profile through July 17, 2003. Progestins (blue line) are in the same range as last week. It is impossible to determine if the high values (100-165 ng/mg Cr) observed on June 24-25 are peak, or just simply high values on a gradual, if erratic, trend upward. We expect peak progestin concentrations to reach the 200-250 ng/mg Cr range, and stay in that range for a couple of weeks. So, we don't believe that we've reached peak concentrations yet, but we must keep an eye on the qualitative trend, which, in the end, will be most informative." The green line above shows estrogen levels; Mei ovulated and Mei and Tian mated just after the peak in early April.

Because a female giant panda cannot detect whether or not she is pregnant, the hormones necessary to support the uterus and fetus during the presumptive time of fetal development are produced whether the female is pregnant or not. This is the hormonal equivalent of an 'insurance policy'—the female is ready just in case she needs to be.

Once urinary progesterone levels begin to decline sharply to baseline, we'll know to be on the alert for an impending birth, on the remote chance that Mei is pregnant. Alternatively, we’ll know when Mei has completed pseduopregnancy. At the moment, our scientists’ best guess is that the urinary progesterone levels will decline in mid- to late-July.

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