2008 Pregnancy Watch

August 6

As of the time we conducted an analysis, we have not collected a sample from today. However, a sample collected last night yielded a progestin value of 31.4 ng/mg Cr., bringing the mean progestin value for yesterday to 32.8 ng/mg Cr.

With progestin values still above baseline values, the luteal phase is not over yet!

 

August 5

One urine sample collected at about eight this morning had a progestin value of about 34 ng/mg Cr. The progestin value today is still above baseline, and considering her behaviors, there is still hope that Mei Xiang’s reproductive cycle may end with a cub.

 

August 4

We have collected and analyzed five samples produced between 1 p.m. yesterday and 6:32 this morning. The progestin concentrations range from 27.2 to 33.3ng/mg Cr. The three additional samples collected yesterday provided a mean progestin value of about 32 ng/mg Cr. The two samples collected today had a mean progestin concentration of about 29 ng/mg Cr.

The progestin concentrations the past couple of days are the lowest since the onset of the secondary rise began in mid-June. Although lower than samples collected just a few days ago, these latest data are still slightly higher than the baseline range pf progestin values, so additional analyses will be needed to conclude an end to the luteal phase.

 

August 3

Two samples were analyzed today, one produced yesterday at 1:45 p.m. and the other from 4:24 this morning. The value for the sample collected yesterday afternoon had a progestin concentration of 50 ng/mg Cr., imperceptibly changing yesterday's mean progestin value (still 51 ng/mg Cr.). The progestin value for the urine excreted early this morning was about 30 ng/mg Cr. Although lower than any recently analyzed sample, this latest progestin value is still slightly above the progestin baseline range, but it is a possible indicator that luteal activity is slowing down. However, as the progestin concentrations are still above the baseline range more analyses are needed until we are confident the luteal phase has come to an end and, until then, a birth is still possible.

 

August 2

Urine voided by Mei Xiang at 1:27 a.m. and 7:35 a.m. today has been collected and analyzed, yielding progestin values of 50 ng/mg Cr. and 52 ng/mg Cr., respectively. The mean progestin value today is 51 ng/mg Cr., which is not very different from yesterday’s progestin value of 53 ng/mg Cr.

The values from today’s samples are still significantly higher than baseline progestin activity, so the luteal phase continues.

 

August 1

Two additional urine samples were collected yesterday, one in the morning and one in the evening, providing a mean progestin value of about 61 ng/mg Cr. A sample collected this morning had a progestin concentration of 53 ng/mg Cr. As yesterday’s mean and today’s progestin values are still higher than baseline range, we can conclude that the luteal phase is not over yet and that there is still hope for a cub.

 

July 31

The luteal phase continues. Urine excreted at about 3:30 a.m. today had a progestin value of 61 ng/mg Cr., a concentration that is slightly higher than the value measured yesterday.

 

July 30

Another two samples were analyzed today. The sample excreted yesterday afternoon had a progestin concentration of 55 ng/mg Cr., bringing yesterday's mean progestin value to 77 ng/mg Cr. The second sample, collected this morning, had a progestin concentration of 51 ng/mg Cr. Both of these values are lower than the values measured yesterday morning. However, these concentrations are still well above baseline—the luteal phase continues.

 

July 29

We have analyzed a urine sample collected from an overnight excretion and another collected this morning. The mean progestin value for those two samples was about 88 ng/mg Cr., up from the mean progestin value from yesterday’s samples (54 ng/mg Cr).

An increase in progestins as the luteal phase comes to an end is not uncommon. However, it does make for a bumpy ride. The duration of the secondary rise is still well within the known durations for secondary rises for giant pandas and everything still looks fine.

 

Another two samples were available for analysis today. The progestin concentration for the sample excreted yesterday morning was about 41 ng/mg Cr. The sample from yesterday afternoon had a progestin concentration of 67 ng/mg Cr., providing a mean progestin concentration of 54 ng/mg Cr.

This overall value is lower than previous day’s progestin values, but still significantly higher than baseline concentrations. The luteal phase continues, and we are kept guessing when it will end.

 

July 28

Two samples were collected yesterday, one in the morning and one in the early evening. The progestin concentrations for these two samples were 63 ng/mg Cr and 74 ng/mg Cr, respectively. The mean progestin value for yesterday was about 68 ng/mg Cr.

These values are similar to values obtained from the samples collected over the past several days, and are still several times higher than baseline concentrations.

Until progestin concentrations approach baseline values, Mei Xiang remains in the luteal phase.

 

July 25

The progestin concentration of a sample collected yesterday morning was about 69 ng/mg Cr. A second sample collected at overnight had about the same progestin value (67 ng/mg Cr). Both of these values are slightly lower than the sample last analyzed (see the July 24 update).

Although the two latest samples showed a decline in progestin concentrations, the reproductive cycle is far from over.

 

July 24

A urine sample from yesterday afternoon contained a progestin value of about 74 ng/mg Cr. This concentrations is higher than the value obtained on July 22, which had a progestin value of about 58 ng/mg Cr.

The continued low values indicate the luteal phase and secondary rise are nearing an end, however an end may not be reached for several more days.

 

July 23

Our analysis of urine excreted last night revealed a progestin concentration of about 58 ng/mg Cr. This value is considerably lower than concentrations obtained since the peak in urinary progestins on July 11. However, this sample was obtained next to some feces and is possibly contaminated with fecal material. Therefore, we will need a fresh clean sample to confirm the trend. If Mei Xiang will provide one for us.

 

July 20

Mei Xiang’s urinary progestin concentrations have not fluctuated much in the past few days. It is unlikely that the luteal phase has concluded. We will continue to monitor for hormonal changes in samples collected over the coming days.

 

July 17

Mei Xiang’s urinary progestin concentrations have increased slightly over the past two days. Although we are still on the tail end of the luteal phase and the secondary rise, the slight increase indicates that this year’s reproductive cycle is not over yet. As more samples become available, we will conduct additional analyses.

 

July 15

Mei Xiang’s urinary progestin concentrations in urine samples collected Sunday and Monday have decreased. From historic data, we know that the time from peak progestin concentration to the return to baseline value is variable, from one to three weeks. That event would signal the end of a pseudopregnancy or coincide with the birth of a cub. We are monitoring Mei's hormones two to three times a week and will provide more updates as data become available.

 

July 13

Mei Xiang’s urinary progestin concentrations continue to increase. Although a drop in progestin values would indicate the end of the luteal phase is near, our data from 2005—when Tai Shan was born—did not reveal this drop: Mei produced infrequent urine samples, which showed progestin concentrations to remain elevated up to the time of parturition (birth). We will continue with hormone analyses on a more frequent basis to track the endocrine changes associated with this phase of her reproductive cycle and provide the best possible index of when we could expect her luteal phase to end.

 

July 10

Mei Xiang’s urinary progestin concentrations continue to increase. The general trend indicates that the end of the luteal phase will be sometime in the next couple weeks. To better track the change in trends over the next few weeks, we will analyze samples more frequently.

 

July 3

Mei Xiang’s urinary progestin concentrations continue to increase. Everything is looking fine and we are still expecting to see increasing progestin concentrations over the next few weeks.

 

June 26

Mei Xiang’s urinary progestins concentrations have increased over the past week, and we are now confident that she has entered the secondary rise period of her luteal phase. Over the next month, we expect further increases in progestin concentrations. As the secondary rise continues, we will be able to further refine the window of when the luteal phase will end—with either the birth of a cub or the end of the pseudopregnancy. We are anticipating an end around late July.

 

June 19

Mei Xiang’s urinary progestins continue at high concentrations. It would be best to look at data we collect over the next week to be more sure about when the onset of the secondary rise occurred. As of today it has been 93 days from the day of the artificial insemination.

 

June 4

The latest hormone data from Mei Xiang have changed very little, indicating that she is still in the primary rise period of her luteal phase. It has been 78 days since the artificial insemination.

 

May 22

The latest urinary hormone data (from yesterday) indicate that Mei Xiang is still in the primary rise period of her luteal phase. It has been 64 days since the artificial insemination.

 

May 8

There has not yet been a significant hormonal change in progestin excretion. Mei Xiang is still in the primary rise period of her luteal phase (learn about the luteal phase). As of today, it has been 57 days since the artificial insemination. See previous years' pregnancy watches to compare Mei's hormone profiles.

 

May 1

Mei Xiang's progestin concentrations still indicate that she is in the primary rise of her luteal phase. Although it is early enough for her to begin the secondary phase and there have been some changes in behavior, her hormonal values at this point do not suggest a change in physiology.

 

April 28

The luteal phase of the giant panda can be divided into two distinct categories based on progestin activity. The first phase of luteal progestin activity immediately follows ovulation (1˚ rise) is characterized by progestin concentrations that are two to ten times greater than baseline levels. For pregnant females, this phase represents the period when the embryo is diapaused and has yet to implant. The duration of the 1˚ rise in Mei Xiang is highly variable and has lasted as long as 104 days and as few as 45 days (see the table below).

The second phase or 2˚ rise is less variable, lasting on average only 42.4 days in Mei Xiang. The progestin concentrations during this phase are significantly higher than those produced during the 1˚ rise, and can be in excess of 30 times baseline concentrations. The shorter and more consistent duration of the 2˚ rise is indicative of embryonic and fetal development.

Although the hormonal dynamics of the luteal phase are similar between pregnant and pseudopregnant females, the analogous parameters are useful in estimating an end to the luteal phase. The variability of the 1˚ rise complicate the determination of an end of the luteal phase, however the 2˚ rise generally lasts between 40 and 50 days. Thereby, determining the onset of the 2˚ rise can provide a window of when the luteal phase is likely to end.

For pregnant females, the end of the luteal phase is parturition (birth of a cub), however for pseudopregnant females the end of the luteal phase is a drop in progestin concentrations with no birthing event. When Mei's 2˚ rise is detected this year, a likely window can be estimated for expecting a possible birth.

Provided below are the endocrine profiles (estrogens indicated in red, progestins in blue) from Mei Xiang’s luteal phases from 2002 to 2008 (we did not measure Mei's hormones in 2006, when she was nursing her year-old cub). The last graph (2008) has the latest endocrine data from Mei Xiang. The black diamonds on the graph represent days of the onset of the 2˚ rise from historic data. The open triangles represent days of the end of the luteal phase (parturition in 2005), also from historic data.

Estrus

Luteal Phase

 

1º Rise

2º Rise

 

Date of
E. Peak

Duration

Date
Ended

Duration

Date
Ended

Total
Duration

2002

4/26

104

8/9

41

9/19

145

2003

4/4

90

7/3

40

8/12

130

2004

5/1

89

7/29

44

9/11

133

2005

3/10

76

5/25

45

7/9

121

2007

4/3

45

5/18

42

6/29

87

2008

3/19


April 10

A significant increase in progestin concentrations has occurred following estrus, a shift that is indicative of corpus luteum (CL) formation. The formation of a CL is necessary for maintenance of the luteal phase, a phase that can be divided into two distinct sub-phases in the giant panda: the primary rise and the secondary rise. Progestin dynamics during the primary rise are highly variable in duration (40-150 days) and magnitude (two to eight times the baseline), and it is also the period of embryonic diapause and before implantation.

It is only after implantation and a subsequent increase in progestin production that the secondary rise begins. Following a more predictable pattern than the primary rise, the secondary rise typically lasts between 40 and 50 days, and is characterized by progestin concentrations in excess of 30 times the baseline levels. Once the secondary rise begins in Mei Xiang, we should have some idea when the luteal phase will conclude (hopefully, with parturition).

We will continue to evaluate hormone patterns to monitor Mei Xiang’s reproductive physiology.

March 27

The increase of progestin levels in excess of the baseline maximal range (>25ng/mg Cr) in samples collected since the March 24 indicates healthy luteal formation. The corpus luteum is the body on the ovary that forms following ovulation and produces most of the progesterone. Formation of a corpus luteum is necessary for maintenance of the luteal phase. We will continue to monitor the hormonal changes associated with Mei Xiang's luteal phase.

As we described last year, the luteal phase serves as a preparatory phase for pregnancy. In most mammals, once the reproductive system has recognized that there is not a fertilized egg and that the female is not pregnant, the luteal phase ends. However, in bears, the luteal cycle lasts the same amount of time whether the female is pregnant or not. As a result, it is very difficult to use hormone analysis to determine whether a bear is pregnant. The giant panda is a bear and, like other bears, it has a luteal cycle that is the same whether or not she is pregnant. Also, as in other bear species, the progesterone profile of the luteal cycle has two phases: a primary rise phase and a secondary rise phase. Following estrus the female begins the primary rise of her luteal cycle.

March 19

The urine sample we collected at 7 a.m. demonstrated a trend of declining estrogens and increasing estrogens.

A subsequent sample collected 40 minutes later was analyzed this afternoon along with a sample collected immediately after artificial insemination (AI). The sample collected at 7:40 a.m. had an estrogen value of 37ng/mg Cr and a progestin value of 19ng/mg Cr. The sample collected at 3 p.m., following the AI, had an estrogen value of 20ng/mg Cr and a progestin value of 27ng/mg Cr.

Using the endocrine database we have developed on Mei Xiang since her arrival at the Zoo years ago, and what is known about giant panda reproduction, we estimate that ovulation occurred some time yesterday afternoon. The period of fertility in the giant panda is about 36 to 48 hours after ovulation. Therefore, these data suggest that artificial insemination was done within the window of fertility.

A note from our reproductive biologist: The artificial insemination was conducted at 2:45 p.m. with semen of excellent quality, good motility, and high concentration.

March 17

The giant panda breeding season is upon us, and Mei Xiang is in estrus. As the giant panda has only one estrus a year and a fertility window of only about 48 hours, we want to identify the time of ovulation as accurately as possible. We use several measures to do this; one of those measures is through monitoring hormonal dynamics associated with estrus. Hormones are the regulators of reproductive function. By assessing hormonal trends through urine analysis, we can track changes in physiology without disturbing Mei.

Typically, estrogen concentrations increase up to the time the female ovulates. Following ovulation, estrogen values drop off, so if we observe a drop in estrogens excreted in the urine, that will be an indicator that ovulation has occurred and that Mei is fertile. However, it is never quite that easy, and some changes in hormone concentrations are not necessarily related to ovarian physiology. Therefore, we also assess progestin concentrations in the urine. Once the female has ovulated, progestin concentrations increase, so we look for both a drop in estrogens and rise in progestins to the estimate time of ovulation.

The dashed line in the graph below represents a threshold of estrogen concentrations. Once estrogen concentrations rise above this line, we know from a hormonal standpoint that Mei Xiang has entered periestrus (the period of time associated with estrus). From the data we've collected over the years, we have learned it takes on average of nine days from the onset of periestrus (the time estrogens surpass the dashed line) to the peak breeding period. The estrogens this year passed the dashed line on March 11. However, Mei Xiang is not obligated to abide by past hormonal trends, and each year we learn something new. So we will keep monitoring hormones and waiting for the estrogens to drop and progestins to rise.

Based on the data obtained from samples collected today, Mei Xiang has not ovulated. Although the estrogens dropped, the progestins did not increase. So it is likely that the drop in the concentrations of both progestins and estrogens is attributed to some nonreproductive physiology.

We will post more data soon as we learn more about her reproductive state.

Read all about the 2007 pregnancy watch.

Page Controls