What do we call the ball of cells which implants into the lining of the uterus?
What substances are passed from mother to baby?
What organ connects mother and baby?
Where does fertilisation occur in the female reproductive system?
A device called an intrauterine device (IUD) can be used by females to prevent pregnancy. It makes the lining of the uterus thinner. Suggest why this stops a pregnancy occurring.
A student’s mother is having another baby. The student says, ‘My mum has been pregnant for 12 weeks. Her embryo is growing really fast.’ What mistake have they made?
Some females suffer from a condition called pre-eclampsia. This condition can cause the placenta to separate from the mother’s uterus. Suggest why pre-eclampsia might mean the fetus needs to be delivered earlier than it would normally be.
Twins
Do you know someone who is a twin? Have you ever wondered how twins are made?
Non-identical twins
Non-identical twins, also known as dizygotic twins, are formed when two separate ova are released from
the ovaries during a woman’s menstrual cycle. This process, known as ovulation, typically results in a
single ovum; however, in the case of non-identical twins, two ova are produced. These ova then travel
down the oviducts, where they can be fertilised by separate sperm cells. If fertilisation is successful, the
fertilised ova, now called zygotes, continue their journey down the oviducts and into the uterus. Once in
the uterus, the zygotes implant themselves into the uterine wall, where they will grow and develop into
fetuses. Because they come from separate ova and sperm, non-identical twins can be of different sexes
and will not be genetically identical.
Identical twins
Identical twins, also known as monozygotic twins, are formed from a single fertilised ovum. During
ovulation, an ovum is released from the ovaries and travels down the oviduct where it can be fertilised
by a sperm cell. This fertilised ovum, now a zygote, then continues down the oviduct and into the uterus.
However, in the case of identical twins, this single zygote will at some point split into two separate but
genetically identical embryos. This split can occur at various stages of early development, but it always
results in two embryos that share the exact same genetic material. These embryos then implant into the
uterine wall and develop into fetuses. Because they come from the same ovum and sperm, identical
twins are always of the same sex and are genetically identical.
IVF and twins
In vitro fertilisation (IVF) is a medical procedure that can increase the likelihood of multiple births,
including twins. During IVF, ova are extracted from the ovaries and fertilised with sperm in a laboratory,
creating one or more embryos. These embryos are then implanted into the uterus. To increase the
chances of a successful pregnancy, often more than one embryo is transferred to the uterus. If two or
more of these implanted embryos successfully implant into the uterine wall and develop, this results in a
multiple pregnancy, potentially leading to twins or even more multiples. It is important to note that
these would be non-identical (dizygotic) twins, as each embryo comes from a separate ovum and sperm.
However, in rare cases, a single IVF embryo could split after implantation, leading to identical
(monozygotic) twins.
What is the difference between identical (monozygotic) and non-identical (dizygotic) twins?
What does the term ‘ovulation’ refer to? How does it relate to the formation of non-identical twins?
Why can non-identical twins be of different sexes, but identical twins cannot?
Science Stories
Sir Robert Edwards, Dr Patrick Steptoe and Jean Purdy:
The inventors of IVF
This story focuses on the collaborative work of some doctors and a nurse to develop a way to help couples
who are unable to have a child naturally to conceive a baby. This story draws on ideas of gametes,
fertilisation and fetal development.
Sir Robert Edwards was a distinguished British scientist born in 1925, often hailed as a pioneer in
reproductive medicine. From a young age, he displayed a curiosity for biology, which led him to study
the subject at the University of Wales and later at the University of Edinburgh. He began his career in a
time when many aspects of human reproduction were still mysteries waiting to be solved.
Sir Robert Edwards, along with Dr Patrick Steptoe and Jean Purdy, dedicated their work to understanding
human fertility. They developed a revolutionary procedure known as in vitro fertilisation (IVF). The
process involves retrieving an egg from a woman’s ovaries, fertilising the egg with sperm in a laboratory
and then implanting the fertilised egg (now an embryo) back into the woman’s uterus. After many
attempts and refinements to their technique, Edwards and Steptoe achieved their landmark success in
1978 with the birth of Louise Brown, the first baby conceived through IVF.
The development of IVF by Edwards, Steptoe and Purdy revolutionised reproductive medicine. It offered
new hope to couples who had been unable to conceive a child naturally. Today, IVF is a common
procedure, helping millions of people worldwide become parents. Their work also opened new areas of
research in reproductive medicine, including genetic screening of embryos, which can help identify and
prevent certain genetic conditions. This groundbreaking procedure has transformed countless lives and
continues to be a crucial part of reproductive medicine.
What is in vitro fertilisation (IVF)?
Who was the first baby conceived through IVF, and when was she born?
Based on the last paragraph, how did the development of IVF influence research in reproductive
medicine?