I have 2 daughters Alhamdulillah. Now me and my family expect one baby boy as my next child, so I can search on Internet and found some method can increasing possibilities of baby boy, like, the woman's diet (alkaline food) plan, her period time calculation, male diet plan, position of intercourse (sex), time of intercourse (sex) and moon night calculation.
So can I follow this method? Is it permissible in Islam?
I know Allah will give me which is better for me, and I will happy with it.
Summary: Gender-selection methods which involve astrology should be avoided (as astrology is forbidden). An Islam Q&A fatwa considers natural methods (such as adjusting one's diet) as permissible. However, it's doubtful that any of these actually work. IVF-based gender selection was considered permissible in a SeekersHub fatwa, but the attitude was "superior to simply leave such matters in the hands of God".
... I can search on internet and found some method can increasing possibilities of baby boy, like , Women diet ( Alkaline food ) plan, her period time calculation, male diet plan, position of intercose ( sex ), time of intercourse ( sex ) and moon night calculation.
It's probably safe to say all of these are pseudoscience and old wives' tales. (I asked about this here Is pseudoscience generally forbidden or discouraged? but it's yet to be answered.)
There's some scientific papers on the topic, e.g. Mathews et al., You are what your mother eats, 2008 (PubMed), which reported "Fifty six per cent of women in the highest third of preconceptional energy intake bore boys, compared with 45% in the lowest third." From the point of view of someone wanting to influence their offspring's sex, this is a very minimal effect. Moreover, the underlying claim is strongly contested:
We examined the hypothesis using new evidence from the wartime famine in Holland in 1944-1945 and failed to show an association between maternal diet in pregnancy and the sex ratio. This makes a causal link highly improbable.
Cramer and Lumey, Maternal preconception diet and the sex ratio, 2010 (PubMed)
(See also Young et al., Cereal-induced gender selection? Most likely a multiple testing false positive, 2009 (PubMed).)
There is a risk, therefore, that this behavior is putting belief in superstitions, which Islam is against in general; see What does Islam say about superstitions? In fact, "Moon night calculation" sounds like a form of astrology, and astrology is definitely forbidden (IslamWeb).
However, Islam Q&A regard natural methods as permissible:
It is permissible to choose the gender of the foetus by natural means, such as following a certain nutrition plan, chemical washes, and choosing times for intercourse according to the time of ovulation, because these are permissible means and there are no reservations about them.
Islam Q&A say that means beyond this are not permissible:
It is not permissible to use any kind of medical intervention to choose the gender of the foetus, except in cases of medical necessity ...
There are methods of gender selection (such as IVF), and a SeekersHub fatwa described this as permissible according to the resolution passed by the Majma al-Fiqh al-Islami in 2007. Based on Qur'an 42:49 (He creates what he wills. He gives to whom He wills female [children], and He gives to whom He wills males), the fatwa goes on to say:
While choosing the gender of a child is not necessarily being discontent with divine decree, it is superior to simply leave such matters in the hands of God.
Muslims believe that every child that comes into the world is created by Allah. He creates according to His will, and it is not our place to question or complain. Our destinies (Qadr) are already written, and every life that comes to be was destined to be by Allah.
On this topic, the Quran says in Surah Shura:
لِّلَّهِ مُلْكُ السَّمَاوَاتِ وَالْأَرْضِ يَخْلُقُ مَا يَشَاءُ يَهَبُ لِمَن يَشَاءُ إِنَاثًا وَيَهَبُ لِمَن يَشَاءُ الذُّكُورَ أَوْ يُزَوِّجُهُمْ ذُكْرَانًا وَإِنَاثًا وَيَجْعَلُ مَن يَشَاءُ عَقِيمًا إِنَّهُ عَلِيمٌ قَدِيرٌ
To Allah belongs the dominion of the heavens and the earth; He creates what he wills. He gives to whom He wills female [children], and He gives to whom He wills males. Or He makes them [both] males and females, and He renders whom He wills barren. Indeed, He is Knowing and Competent.
W.r.t your query on gender, an indirectly related Hadith:
Narrated Anas:
When Abdullah bin Salam heard the arrival of the Prophet (ﷺ) at Medina, he came to him and said, "I am going to ask you about three things which nobody knows except a prophet:
1) What is the first portent of the Hour?
2) What will be the first meal taken by the people of Paradise?
3) Why does a child resemble its father, and why does it resemble its maternal uncle"
Allah's Messenger (ﷺ) said, "Gabriel has just now told me of their answers."
Abdullah said, "He (i.e. Gabriel), from amongst all the angels, is the enemy of the Jews."
Allah's Messenger (ﷺ) said, "The first portent of the Hour will be a fire that will bring together the people from the east to the west; the first meal of the people of Paradise will be Extra-lobe (caudate lobe) of fish-liver.
As for the resemblance of the child to its parents: If a man has sexual intercourse with his wife and gets discharge first, the child will resemble the father, and if the woman gets discharge first, the child will resemble her."
On that Abdullah bin Salam said, "I testify that you are the Messenger of Allah."
Abdullah bin Salam further said, "O Allah's Messenger (ﷺ)! The Jews are liars, and if they should come to know about my conversion to Islam before you ask them (about me), they would tell a lie about me."
The Jews came to Allah's Messenger (ﷺ) and Abdullah went inside the house. Allah's Apostle asked (the Jews), "What kind of man is Abdullah bin Salam amongst you?" They replied, "He is the most learned person amongst us, and the best amongst us, and the son of the best amongst us."
Allah's Messenger (ﷺ) said, "What do you think if he embraces Islam (will you do as he does)?"
The Jews said, "May Allah save him from it."
Then Abdullah bin Salam came out in front of them saying, "I testify that None has the right to be worshipped but Allah and that Muhammad is the Apostle of Allah." Thereupon they said, "He is the evilest among us, and the son of the evilest amongst us," and continued talking badly of him.
for a simple answer
So it is not permissible to change diet with that intention. If Quran/Hadith is silent on a matter and medical science gives a direction, then one can go with medical science.
But here neither Quran/hadith has given a diet for this, nor medical science has a recommended diet. So the answer is simple -- not permissible.
But if still someone goes with some diet thinking that it will change the gender, then that is bidah (innovation in religion). Innovation in religion is a sin, unless it is a good innovation.
