The king gets Rishysringa (Sarga 11) who performs the ceremony. The ceremony goes off very gloriously and well. (Sargas 12,13, and 14)

Meanwhile, the gods are having a problem. The Rakshasa (demon) known as Ravana was causing a huge problem because, due to a boon he had received from Brahma, he was invincible to gods, celestial snakes, and devils. The gods ask Narayana (Vishnu) what to do and he decides to incarnate himself on earth as a man- when Ravana had asked for his boon, the foolish demon had forgotten to mention protection from men. Vishnu thereupon incarnates himself as celestial porridge and has himself handed by to Dasharatha by a red colored being who appeared out of Rishysringa's sacrificial fire. The being (usually taken to be Agni, the god of Fire) tells Dasharatha to give the porridge to his wives. Dasharatha gives the porridge to his three queens (his three main wives), and they give birth to four sons between the three of them: Queen Kaushalya gives birth to baby Rama, Queen Kaikeyi gives birth to baby Bharata, and Queen Sumitra gives birth to twins: baby Shatrughna and baby Lakshmana. The book details the miraculous birth of Rama and his brothers Lakshmana, Bharata and Shatrughna, their early life in Ayodhya and education with Rishi Vasishtha. Also included are Rama's slaying of the demoness Tataka of the forest, his slaying of the demon Subahu and his hordes who defile the yajnas of Vishvamitra, his deliverance of Ahalya and his wedding with Sita.

"ततो यज्ञे समाप्ते तु ऋतूनाम् षट् समत्ययुः ।
ततः च द्वादशे मासे चैत्रे नावमिके तिथौ ॥१-१८-८॥
नक्क्षत्रे अदिति दैवत्ये स्व उच्छ संस्थेषु पंचसु ।
ग्रहेषु कर्कटे लग्ने वाक्पता इंदुना सह ॥१-१८-९॥
प्रोद्यमाने जगन्नाथम् सर्व लोक नमस्कृतम् ।
कौसल्या अजनयत् रामम् सर्व लक्षण संयुतम् ॥१-१८-१०॥
विष्णोः अर्धम् महाभागम् पुत्रम् ऐक्ष्वाकु नंदनम् ।
लोहिताक्षम् महाबाहुम् रक्त ओष्टम् दुंदुभि स्वनम् ॥१-१८-११॥
^[1]

“On completion of the ritual six seasons have passed by
and then in the twelfth month,
on the ninth day of Chaitra month [April-May,]
when the presiding deity of ruling star of the day is Aditi,
where the ruling star of day is Punarvasu (Nakshatra),
the asterism is in the ascendant, and when five of the nine planets viz.,
Sun, Mars, Jupiter, Saturn, and Venus are at their highest position,
when Jupiter with Moon is ascendant in Cancer, and when day is advancing,
then Queen Kausalya gave birth to a son with all the divine attributes like
lotus-red eyes, lengthy arms, roseate lips, voice like drumbeat,
and who took birth to delight the Ikshwaku dynasty,
who is adored by all the worlds,
and who is the greatly blessed epitome of Vishnu, namely Rama.”
- Book I : Bala Kanda, Ramayana by Valmiki, Chapter (Sarga) 18, Verse 8, 9, 10 and 11 ^[2]