How can fertility be increased or decreased, and how do these methods work?
The biology of controlling fertility, including cyclical and continuous fertility, treatments for infertility (ovulation-stimulating and superovulatory drugs, artificial insemination, IVF, ICSI and pre-implantation genetic diagnosis) and methods of contraception (physical, chemical and surgical).
An SQA Higher Human Biology answer on the biology of controlling fertility, covering cyclical and continuous fertility, fertile periods, treatments for infertility (stimulating ovulation, IVF, ICSI and pre-implantation genetic diagnosis), artificial insemination, and physical, chemical and surgical methods of contraception.
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What this dot point is asking
The SQA wants you to explain cyclical and continuous fertility, describe treatments for infertility (stimulating ovulation, artificial insemination, IVF, ICSI and pre-implantation genetic diagnosis), and describe how physical, chemical and surgical methods of contraception work.
Cyclical and continuous fertility
A female's fertile period spans the days around ovulation, because an ovum survives only a short time and sperm can survive a few days in the female tract. Knowing when fertility is highest helps couples either to conceive or to avoid conception, and underlies several methods of controlling fertility.
Treating infertility
When a couple cannot conceive naturally, several treatments can raise the chance of fertilisation:
- Stimulating ovulation. Drugs that mimic or boost FSH and LH can stimulate ovulation in women who do not ovulate regularly. Superovulatory drugs cause several ova to mature at once, which is needed for IVF.
- Artificial insemination. Semen, sometimes from a donor, is placed directly into the female reproductive tract. This helps when the man has a low sperm count, because the sperm are concentrated and delivered close to the ovum.
- In vitro fertilisation (IVF). After superovulation, ova are collected and mixed with sperm in a dish so fertilisation occurs outside the body. The resulting embryos are cultured for a few days, and one or two healthy embryos are transferred into the uterus.
- ICSI (intracytoplasmic sperm injection). A single sperm is injected directly into the cytoplasm of an ovum. This is used when sperm are too few, abnormal or unable to penetrate the egg.
Contraception
Contraception decreases fertility and works in three main ways:
- Physical (barrier) methods prevent sperm reaching the ovum, for example the condom or diaphragm. Some, such as the intrauterine device, prevent implantation.
- Chemical methods use hormones. The combined oral contraceptive pill contains oestrogen and progesterone, whose continuous high level inhibits FSH and LH by negative feedback. With FSH inhibited no follicle develops, and with the LH surge prevented there is no ovulation, so fertilisation cannot occur.
- Surgical methods are permanent. Vasectomy cuts the tubes carrying sperm in the male, and tubal ligation cuts or blocks the oviducts in the female, so gametes cannot meet.
Examples in context
Example 1. Superovulation for IVF. A woman undergoing IVF is given FSH-like drugs so that many follicles mature together. Collecting several ova at once raises the chance that at least one healthy embryo can be created and transferred, showing how stimulating fertility supports treatment.
Example 2. PGD for an inherited disorder. A couple who both carry a recessive disease-causing allele use IVF with PGD. Each embryo is tested and only those that will not develop the disorder are transferred, reducing the chance of an affected child.
Try this
Q1. State whether males are cyclically or continuously fertile. [1 mark]
- Cue. Continuously fertile.
Q2. Explain why the combined pill prevents ovulation. [1 mark]
- Cue. Its oestrogen and progesterone inhibit FSH and LH by negative feedback, so no follicle develops and no LH surge triggers ovulation.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA Higher 20193 marksExplain how the combined oral contraceptive pill prevents pregnancy.Show worked answer →
A 3-mark answer needs the hormones in the pill and their effect by feedback.
The combined pill contains oestrogen and progesterone. The continuous high level of these hormones acts on the pituitary gland by negative feedback, inhibiting the release of FSH and LH.
Because FSH is inhibited, no follicle is stimulated to develop, and because the LH surge is prevented, ovulation does not occur. With no ovum released, fertilisation cannot take place.
Award (1) the pill contains oestrogen and progesterone, (2) these inhibit FSH and LH by negative feedback, and (3) without FSH and the LH surge there is no follicle development or ovulation.
SQA Higher 20214 marksDescribe the steps involved in in vitro fertilisation (IVF) and explain why ICSI may be used instead of standard IVF.Show worked answer →
This is a 4-mark question on assisted reproduction.
In IVF, the woman is first given hormones to cause superovulation, so several ova mature at once. The ova are collected from the ovaries and mixed with sperm in a dish so that fertilisation takes place outside the body. The resulting embryos are cultured for a few days, and one or two healthy embryos are then transferred into the uterus.
ICSI (intracytoplasmic sperm injection) is used when the man's sperm are few, abnormal or unable to penetrate the ovum. A single sperm is injected directly into the cytoplasm of the ovum to achieve fertilisation, overcoming the sperm defect.
Award (1) hormones cause superovulation and ova are collected, (2) ova and sperm mixed so fertilisation occurs outside the body, (3) a healthy embryo is transferred to the uterus, and (4) ICSI injects one sperm into the ovum when sperm quality or count is too low.
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