The New Zealand Study

Introduction

The actual name of the study is "A prospective study of the preselection of the sex of offspring by timing intercourse relative to ovulation," and it was carried out in Aukland, New Zealand, and published in the medical journal Fertility and Sterility in June, 1984. (Yes, that's 29 years ago.)

The study's purpose was to see whether a baby's gender can be determined by timing intercourse relative to ovulation, as claimed by Shettles. A number of couples were instructed to track several ovulation indicators, and to time intercourse using the Shettles theory.

The results seem to refute Shettles, because a significantly larger number of boys were conceived 3 to 5 days before ovulation. This indicates that the Y-bearing sperm, did not, as Shettles contends, have only a short survival time. Only 39% of the 33 couples completing the study conceived the gender they desired.

While 33 births is a small number for statistical analysis, this study is one of the few closely monitored investigations (that I have found) into the relationship between the timing of intercourse relative to ovulation, and the gender outcome.

Participants

Couples who wished to choose the sex of their baby were recruited. Many had probably heard of the Shettles method, because an article featuring Shettles had recently appeared in a popular magazine. Although 185 participants began the study, data from only 33 pregnancies was used in the study. Here's why:

185	ORIGINAL PARTICIPANTS
- 85	Quit the study (decided not to get pregnant, or just wimped out of the study)
- 30	Not yet pregnant (at time of report)
- 4	Discontinued from study (not pregnant after 6 cycles
66	TOTAL PREGNANCIES
- 4	Miscarriages
- 1	Ectopic Pregnancy
- 9	Still pregnant (at time original study was concluded)
55	BABIES BORN
- 19	Excluded because had intercourse more than once during cycle (against instructions!)
33	BIRTHS IN STUDY (22 boys, 11 girls)

More about these 33 remaining couples:

• Mother's Age: 22 to 35 years, with an average of 29.7 years
  Father's Age: 26 to 48 years, with an average of 32.5 years

• Before the study, the couples had an average of 2 children, with 1.3 times more sons than daughters.

• 19 couples wanted girls, and 14 wanted boys.

• On average, it took couples 2 active cycles to get pregnant. 15 couples (45%) became pregnant the first cycle.

About the 4 miscarriages and ectopic pregnancy:

• These occurred in the first trimester, and appeared to be no different than those commonly seen.
• Three were conceived 3 days before ovulation, one was 2 days before ovulation, and one at ovulation. The researchers concluded there was no data to support the theory that miscarriages are more likely with "over-aged" sperm.

An extension to the study provided data for an additional 22 births, some of which is shown in the results below.

Ovulation Indicators

Women in the study were asked to track and chart the following ovulation indicators to determine the day of ovulation:

1. Basal body temperature (BBT)
2. Cervical mucus (CM)
3. Leutenizing hormone (LH) surge

To be able to anticipate ovulation, each woman was instructed by an accredited teacher of the New Zealand Association of Natural Family Planning. The woman was taught how to observe and chart her CM and BBT, and continued to meet monthly with her teacher to review her charts throughout the study. The study began with up to three practice cycles (during which couples did not try to become pregnant) while the woman learned to track CM and BBT.

To monitor the third indicator, LH surge, the woman collected her first morning urine from the onset of the fertile period until 3 days after peak CM. (Although the study doesn't specifically mention how LH surge was detected, I assume the LH in the urine was measured in a lab, not using any sort of home kit like the OPKs we have available today.)

Intercourse Instructions

Couples were advised as follows:

• Abstain from intercourse from the onset of fertile CM or from cycle day 7, whichever comes first.
• To try for a son, have intercourse on the day after peak CM is observed.
  To try for a daughter, have intercourse 2 or 3 days before peak CM is anticipated, using previous month's charts to predict.
• Have intercourse once only during the fertile period, and abstain until at least the 5th day after peak CM. (This was to ensure that there was no doubt about which day of intercourse resulted in conception.)

However, although Shettles makes the following recommendations, couples were not advised to try them (due to a lack of any supporting evidence):

• Altering vaginal pH with an alkaline or acidic douche
• Intentionally avoiding or achieving female orgasm
• Using a particular intercourse position or degree of penetration

Study Results

Because the ovulation indicators tracked in this study don't show the exact moment of ovulation, the gender outcome was evaluated seperately against each of the three ovulation indicators. (It was assumed that the actual fertilization occurred 5 to 8 hours after ovulation, based on observations during in vitro studies.)

The charts below show the number of babies born of each gender, against the number of days between intercourse and ovulation. (A negative number indicates days before ovulation, and a positive number indicates days after ovulation.) Also, the additional 22 births from the extension of the study are included in the first two charts, although it is not available for the last chart.

Key to charts:
= Girls, Original Study
= Girls, Followup Study
= Boys, Original Study
= Boys, Followup Study

Results by
LH Surge

Results by Peak CM

Results by BBT Shift

Study Data

The chart below shows the cycle day reported by each woman for intercourse (BD) and the three ovulation indicators. The "Days Between BD and O" columns are computed thus:
    By LH Surge = BD Cycle Day - LH Surge Cycle Day - 1
    By CM Peak = BD Cycle Day - CM Peak Cycle Day - 1
    By BBT Shift = BD Cycle Day - BBT Shift Cycle Day + 1

(Several anomalies I noticed in the data are highlighted in red. These are either errors in reporting the data, or errors in doing the arithmetic to compute O day. More about that below.)

Subject	Cycle Day				Days Between BD and O			Baby
	BD	LH Surge	CM Peak	BBT Shift	By LH Surge	By CM Peak	By BBT Shift
1.	12	16	15	18	-5	-4	-5	M
2.	16	20	16	22	-5	-1	-5	M
3.	14	18	17	15	-5	-4	0	M
4.	13	17	16	18	-5	-4	-4	M
5.	12	15	16	17	-4	-5	-4	M
6.	9	12	11	13	-4	-3	-3	F
7.	11	13	15	14	-3	-5	-2	M
8.	10	12	12	12	-3	-3	-1	M
9.	18	20	22	22	-3	-5	-3	M
10.	15	17	17	18	-3	-3	-2	M
11.	14	16	13	Monophasic	-3	0	NA	M
12.	9	11	14	No Chart	-3	-6	NA	M
13.	15	17	17	19	-3	-3	-2	F
14.	11	13	12	15	-3	-2	-3	F
15.	11	12	11	12	-2	-1	0	M
16.	11	12	12	13	-2	-2	-1	M
17.	17	18	20	16	-2	-4	2	M
18.	13	14	15	16	-2	-3	-2	M
19.	14	15	14	16	-2	-1	-1	F
20.	12	12	14	14	-1	-3	-1	M
21.	14	14	15	15	-1	-2	0	M
22.	15	15	16	17	-1	-2	-1	M
23.	17	17	19	19	-1	-2	-1	M
24.	18	18	18	20	-1	-1	-1	M
25.	15	15	17	No Chart	-1	-3	NA	M
26.	16	16	16	19	-1	-1	-2	M
27.	14	14	16	15	-1	-3	0	F
28.	16	14	14	17	0	0	0	F
29.	13	12	13	14	0	-1	0	F
30.	14	13	12	14	0	1	1	F
31.	27	26	26	28	0	0	0	F
32.	18	17	18	19	0	-1	0	F
33.	13	11	14	13	1	-2	1	F

Evaluation

Everything above comes directly from the study. Below are some of my own observations.

Data Anomalies

We have no way of knowing whether these are simply due to a typo in reporting the original data, or an actual error in arithmetic. The latter would mean that the preceding charts are incorrect!

• Subject #13: If her BBT Shift was on day 19, the days between BD and O (by BBT Shift) would be -3, not -2. (And -3 agrees with her other O indicators.)
• Subject #23: If her CM Peak was on day 19, the days between BD and O (by CM Peak) would be -3, not -2.
• Subject #28: If her LH Surge was on day 14, the days between BD and O (by LH Surge) would be 1, not 0.
  Also, if her CM peak was on day 14, the days between BD and O (by CM Peak) would be 1, not 0.

Variations in Computed O Day

The researchers simply computed O day three separate times, based on 3 separate indicators. Sometimes the results varied widely! Look at subject #1. Her O is computed to be CD 21 by both LH Surge and BBT Shift, but 4 days earlier by CM Peak. This means that this subject appears in the -5 days column in charts 1 and 3, but in the -1 days column on chart 2!

Wimpy Subjects

Out of the original 185 participants, the vast majority decided they couldn't handle the rigors of the study (charting BBT, abstaining from intercourse, etc.) These people didn't have 1% of the grit and determination I see every day on the gender determination boards! I'd like to smack 'em!