"I want to ask you a question concerning
something. I am married, and have been for four weeks.
I have been taking birth control (although not on
time sometimes) but I have been having some suspicion
that I am pregnant. I have stopped taking birth control
in case this is true, but I was wondering how long
I need to be off birth control before I can go get
a pregnancy test at the doctor's office. I figure
that since the tests tell if you are pregnant by the
hormone levels, and since birth control raises the
hormone, estrogen in the body, I might need to wait
a while before getting a test done so that I can get
a truthful answer. I am aware that birth control can
give me symptoms that make me think I'm pregnant,
but I have a feeling it may not just be birth control.
Please give me your opinion as to what I should do
if you can ". Mary
Birth control pills, the combined estrogen and progestin
pills as opposed to progestin only pills, have a very
good record of preventing pregnancy. If a woman takes
the pills regularly and is not late or misses any,
the pregnancy rate is only 1 per 1000 women (0.1%).
No one is perfect however, so the typical use pregnancy
rate is higher. Some studies indicate a 3% pregnancy
rate and others indicate as high as 5%. Therefore,
concern about possibly becoming pregnant while taking
pills is common.
Will taking birth control pills make a pregnancy
test inaccurate?
No. Pregnancy tests are NOT interfered with by the
hormones of oral contraceptives. You are correct that
estrogens are elevated in pregnancy and birth control
pills contain estrogens, but that is not the hormone
that is measured to determine pregnancy. All pregnancy
tests measure the beta subunit of a placental hormone
called human chorionic gonadotropin (HCG). You will
often see it abbreviated as beta HCG. It can be measured
in the urine or blood. While it depends upon the sensitivity
of the specific test, most home urine pregnancy tests
(sensitive to 25 mIU) will turn positive about 13-16
days after conception. If you were not on oral contraceptives,
this would mean about the time of the first missed
menses. When you are on oral contraceptives, ovulation
could have occurred at more irregular times so that
all you can say is if the pregnancy test is negative,
you are either not pregnant or are less than about
14 days pregnant from ovulation.
How likely is it to get pregnant with missing pills
or being late in taking them?
There are many reasons why women may not take their
birth control pill on time or even miss them entirely.
Such reasons for missing pills include disruptions
in their daily routines, their husband's absence,
spotting, and just trouble remembering to take them
each day. If you are missing pills, you are not alone.
One study shows 47% of women missing >=1 pill per
cycle and almost a quarter (22%) missing >=2 pills
per cycle. Even though this rate of missing pills
commonly happens, it is still unlikely to get pregnant.
In women off pills for 10 days, only about one in
ten will ovulate.
While it is normal to be concerned about possible
pregnancy when missing pills, most women can be reassured
that they will not get pregnant as long as they do
not continue to stay off of the pills.
If I miss some pills in a cycle, should I take them
or just stop and wait for my menses?
Ovulation does not usually occur within the first
4 days of missing pills (2). For many women, however,
by the third day of missing pills a menses will usually
have started. If you have just missed one pill, take
that pill (yesterday's) and today's pill both together
and just continue on as per your normal schedule.
If you have missed 2-4 pills and just have spotting,
you should go ahead and resume taking the pills you
are supposed to be on and finish out the pack. Even
though the odds are still in your favor not to get
pregnant, most doctors would advise you to use back
up contraception (condoms/foam) over the next seven
days or abstain from further intercourse until that
cycle is over.
If your menses has fully started, just stay off of
the pills until you have been off for seven days and
then start a new birth control pill pack.
What happens if I was taking oral contraceptives
when I was already pregnant?
While no one would intentionally take oral contraceptives
if they knew they were pregnant, many women each year
inadvertently take pills being unaware they are already
pregnant. In the U.S. and Europe, in approximately
2-5% of all pregnancies mothers have a history of
having taken birth control pills without realizing
they were pregnant. Many years ago, with higher dose
contraceptive pills, there were concerns that the
hormones in pills could produce genital changes in
both male and female babies. Subsequent studies have
failed to confirm this. At the Hospital for Sick Children
in Toronto, Canada, the Motherisk program which tracks
various birth defects, there is a good article on
oral contraceptives and their effect on pregnancy
(3). This article suggests that there is no need to
be concerned about the pills causing birth defects
any more than the background rate of birth defects
that normally occurs.
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